diff --git a/src/common/string.h b/src/common/string.h
index 5cb2fdba6..9a344ce2e 100644
--- a/src/common/string.h
+++ b/src/common/string.h
@@ -1,4 +1,5 @@
 #pragma once
+#include "fmt/core.h"
 #include "types.h"
 #include <algorithm>
 #include <cstdarg>
@@ -6,6 +7,7 @@
 #include <limits>
 #include <string>
 #include <string_view>
+#include <utility>
 
 //
 // String
@@ -38,6 +40,8 @@ public:
   };
 
 public:
+  using value_type = char;
+
   // Creates an empty string.
   String();
 
@@ -107,6 +111,9 @@ public:
   void AppendFormattedString(const char* FormatString, ...) printflike(2, 3);
   void AppendFormattedStringVA(const char* FormatString, va_list ArgPtr);
 
+  template<typename... T>
+  void AppendFmtString(fmt::format_string<T...> fmt, T&&... args);
+
   // append a single character to this string
   void PrependCharacter(char c);
 
@@ -125,6 +132,9 @@ public:
   void PrependFormattedString(const char* FormatString, ...) printflike(2, 3);
   void PrependFormattedStringVA(const char* FormatString, va_list ArgPtr);
 
+  template<typename... T>
+  void PrependFmtString(fmt::format_string<T...> fmt, T&&... args);
+
   // insert a string at the specified offset
   void InsertString(s32 offset, const String& appendStr);
   void InsertString(s32 offset, const char* appendStr);
@@ -136,6 +146,9 @@ public:
   void Format(const char* FormatString, ...) printflike(2, 3);
   void FormatVA(const char* FormatString, va_list ArgPtr);
 
+  template<typename... T>
+  void Fmt(fmt::format_string<T...> fmt, T&&... args);
+
   // compare one string to another
   bool Compare(const String& otherString) const;
   bool Compare(const char* otherText) const;
@@ -283,6 +296,9 @@ public:
   bool operator>(const String& compString) const { return (NumericCompare(compString) > 0); }
   bool operator>(const char* compString) const { return (NumericCompare(compString) > 0); }
 
+  // STL adapters
+  ALWAYS_INLINE void push_back(value_type&& val) { AppendCharacter(val); }
+
 protected:
   // Internal append function.
   void InternalPrepend(const char* pString, u32 Length);
@@ -358,6 +374,14 @@ public:
     return returnValue;
   }
 
+  template<typename... T>
+  static StackString FromFmt(fmt::format_string<T...> fmt, T&&... args)
+  {
+    StackString ret;
+    fmt::vformat_to(std::back_inserter(ret), fmt, fmt::make_format_args(args...));
+    return ret;
+  }
+
   // Will use the string data provided.
   StackString& operator=(const StackString& copyString)
   {
@@ -415,3 +439,24 @@ typedef StackString<512> PathString;
 
 // empty string global
 extern const String EmptyString;
+
+template<typename... T>
+void String::AppendFmtString(fmt::format_string<T...> fmt, T&&... args)
+{
+  fmt::vformat_to(std::back_inserter(*this), fmt, fmt::make_format_args(args...));
+}
+
+template<typename... T>
+void String::PrependFmtString(fmt::format_string<T...> fmt, T&&... args)
+{
+  TinyString str;
+  fmt::vformat_to(std::back_inserter(str), fmt, fmt::make_format_args(args...));
+  PrependString(str);
+}
+
+template<typename... T>
+void String::Fmt(fmt::format_string<T...> fmt, T&&... args)
+{
+  Clear();
+  fmt::vformat_to(std::back_inserter(*this), fmt, fmt::make_format_args(args...));
+}
diff --git a/src/core/cheevos.cpp b/src/core/cheevos.cpp
index 8cf5c2064..ffa3e1934 100644
--- a/src/core/cheevos.cpp
+++ b/src/core/cheevos.cpp
@@ -23,6 +23,7 @@
 #include <algorithm>
 #include <cstdarg>
 #include <cstdlib>
+#include <ctime>
 #include <functional>
 #include <string>
 #include <vector>
@@ -539,7 +540,7 @@ void Cheevos::LoginCallback(s32 status_code, const FrontendCommon::HTTPDownloade
     g_host_interface->GetSettingsInterface()->SetStringValue("Cheevos", "Username", username.c_str());
     g_host_interface->GetSettingsInterface()->SetStringValue("Cheevos", "Token", login_token.c_str());
     g_host_interface->GetSettingsInterface()->SetStringValue(
-      "Cheevos", "LoginTimestamp", TinyString::FromFormat("%" PRIu64, Timestamp::Now().AsUnixTimestamp()));
+      "Cheevos", "LoginTimestamp", TinyString::FromFormat("%" PRIu64, static_cast<u64>(std::time(nullptr))));
     g_host_interface->GetSettingsInterface()->Save();
   }
 
diff --git a/src/core/host_interface.cpp b/src/core/host_interface.cpp
index 67743e55b..73ae20d0f 100644
--- a/src/core/host_interface.cpp
+++ b/src/core/host_interface.cpp
@@ -11,6 +11,7 @@
 #include "cpu_code_cache.h"
 #include "cpu_core.h"
 #include "dma.h"
+#include "fmt/chrono.h"
 #include "gpu.h"
 #include "gte.h"
 #include "host_display.h"
@@ -949,11 +950,7 @@ std::string HostInterface::GetProgramDirectoryRelativePath(const char* format, .
 
 TinyString HostInterface::GetTimestampStringForFileName()
 {
-  const Timestamp ts(Timestamp::Now());
-
-  TinyString str;
-  ts.ToString(str, "%Y-%m-%d_%H-%M-%S");
-  return str;
+  return TinyString::FromFmt("{:%Y-%m-%d_%H-%M-%S}", fmt::localtime(std::time(nullptr)));
 }
 
 std::string HostInterface::GetMemoryCardDirectory() const
diff --git a/src/frontend-common/common_host_interface.cpp b/src/frontend-common/common_host_interface.cpp
index cc5623040..6ebb77c7d 100644
--- a/src/frontend-common/common_host_interface.cpp
+++ b/src/frontend-common/common_host_interface.cpp
@@ -3094,7 +3094,8 @@ std::vector<CommonHostInterface::SaveStateInfo> CommonHostInterface::GetAvailabl
     if (!FileSystem::StatFile(path.c_str(), &sd))
       return;
 
-    si.push_back(SaveStateInfo{std::move(path), sd.ModificationTime.AsUnixTimestamp(), static_cast<s32>(slot), global});
+    si.push_back(SaveStateInfo{std::move(path), static_cast<std::time_t>(sd.ModificationTime.AsUnixTimestamp()),
+                               static_cast<s32>(slot), global});
   };
 
   if (game_code && std::strlen(game_code) > 0)
@@ -3119,7 +3120,7 @@ std::optional<CommonHostInterface::SaveStateInfo> CommonHostInterface::GetSaveSt
   if (!FileSystem::StatFile(path.c_str(), &sd))
     return std::nullopt;
 
-  return SaveStateInfo{std::move(path), sd.ModificationTime.AsUnixTimestamp(), slot, global};
+  return SaveStateInfo{std::move(path), static_cast<std::time_t>(sd.ModificationTime.AsUnixTimestamp()), slot, global};
 }
 
 std::optional<CommonHostInterface::ExtendedSaveStateInfo>
diff --git a/src/frontend-common/common_host_interface.h b/src/frontend-common/common_host_interface.h
index 574c48226..b538bed1a 100644
--- a/src/frontend-common/common_host_interface.h
+++ b/src/frontend-common/common_host_interface.h
@@ -4,6 +4,7 @@
 #include "core/controller.h"
 #include "core/host_interface.h"
 #include <atomic>
+#include <ctime>
 #include <functional>
 #include <map>
 #include <memory>
@@ -78,7 +79,7 @@ public:
   struct SaveStateInfo
   {
     std::string path;
-    u64 timestamp;
+    std::time_t timestamp;
     s32 slot;
     bool global;
   };
@@ -89,7 +90,7 @@ public:
     std::string title;
     std::string game_code;
     std::string media_path;
-    u64 timestamp;
+    std::time_t timestamp;
     s32 slot;
     bool global;
 
diff --git a/src/frontend-common/fullscreen_ui.cpp b/src/frontend-common/fullscreen_ui.cpp
index 603e36454..aab2a315e 100644
--- a/src/frontend-common/fullscreen_ui.cpp
+++ b/src/frontend-common/fullscreen_ui.cpp
@@ -20,6 +20,8 @@
 #include "core/resources.h"
 #include "core/settings.h"
 #include "core/system.h"
+#include "fmt/chrono.h"
+#include "fmt/format.h"
 #include "fullscreen_ui_progress_callback.h"
 #include "game_list.h"
 #include "icon.h"
@@ -2391,12 +2393,12 @@ void DrawSettingsWindow()
           ActiveButton(SmallString::FromFormat(ICON_FA_USER "  Username: %s", Cheevos::GetUsername().c_str()), false,
                        false, ImGuiFullscreen::LAYOUT_MENU_BUTTON_HEIGHT_NO_SUMMARY);
 
-          Timestamp ts;
           TinyString ts_string;
-          ts.SetUnixTimestamp(StringUtil::FromChars<u64>(s_host_interface->GetSettingsInterface()->GetStringValue(
-                                                           "Cheevos", "LoginTimestamp", "0"))
-                                .value_or(0));
-          ts.ToString(ts_string, "%Y-%m-%d %H:%M:%S");
+          ts_string.AppendFmtString(
+            "{:%Y-%m-%d %H:%M:%S}",
+            fmt::localtime(StringUtil::FromChars<u64>(
+                             s_host_interface->GetSettingsInterface()->GetStringValue("Cheevos", "LoginTimestamp", "0"))
+                             .value_or(0)));
           ActiveButton(SmallString::FromFormat(ICON_FA_CLOCK "  Login token generated on %s", ts_string.GetCharArray()),
                        false, false, ImGuiFullscreen::LAYOUT_MENU_BUTTON_HEIGHT_NO_SUMMARY);
           ImGui::PopStyleColor();
@@ -2767,9 +2769,7 @@ void InitializeSaveStateListEntry(SaveStateListEntry* li, CommonHostInterface::E
     li->title = StringUtil::StdStringFromFormat("%s Slot %d##game_slot_%d", ssi->title.c_str(), ssi->slot, ssi->slot);
   }
 
-  li->summary =
-    StringUtil::StdStringFromFormat("%s - Saved %s", ssi->game_code.c_str(),
-                                    Timestamp::FromUnixTimestamp(ssi->timestamp).ToString("%c").GetCharArray());
+  li->summary = fmt::format("{} - Saved {:%c}", ssi->game_code.c_str(), fmt::localtime(ssi->timestamp));
 
   li->slot = ssi->slot;
   li->global = ssi->global;
diff --git a/src/frontend-common/save_state_selector_ui.cpp b/src/frontend-common/save_state_selector_ui.cpp
index 3260fa9b5..214418d56 100644
--- a/src/frontend-common/save_state_selector_ui.cpp
+++ b/src/frontend-common/save_state_selector_ui.cpp
@@ -4,6 +4,8 @@
 #include "common/timestamp.h"
 #include "core/host_display.h"
 #include "core/system.h"
+#include "fmt/chrono.h"
+#include "fmt/format.h"
 #include "icon.h"
 #include "imgui.h"
 Log_SetChannel(SaveStateSelectorUI);
@@ -146,7 +148,7 @@ void SaveStateSelectorUI::InitializeListEntry(ListEntry* li, CommonHostInterface
   li->title = std::move(ssi->title);
   li->game_code = std::move(ssi->game_code);
   li->path = std::move(ssi->path);
-  li->formatted_timestamp = Timestamp::FromUnixTimestamp(ssi->timestamp).ToString("%c");
+  li->formatted_timestamp = fmt::format("{:%c}", fmt::localtime(ssi->timestamp));
   li->slot = ssi->slot;
   li->global = ssi->global;