Actually managed to add SDL2 support somehow

src/dawnsdl2/time/CMakeLists.txt

@@ -0,0 +1,10 @@
+# Copyright (c) 2022 Dominic Masters
+# 
+# This software is released under the MIT License.
+# https://opensource.org/licenses/MIT
+
+# Sources
+target_sources(${DAWN_TARGET_NAME}
+  PRIVATE
+    TimeManager.cpp
+)

src/dawnsdl2/time/TimeManager.cpp

@@ -0,0 +1,16 @@
+// Copyright (c) 2022 Dominic Masters
+// 
+// This software is released under the MIT License.
+// https://opensource.org/licenses/MIT
+
+#include "TimeManager.hpp"
+
+using namespace Dawn;
+
+TimeManager::TimeManager() : ITimeManager() {
+
+}
+
+int64_t TimeManager::getTimestamp() {
+  return (int64_t)std::time(nullptr);
+}

src/dawnsdl2/time/TimeManager.hpp

@@ -0,0 +1,15 @@
+// Copyright (c) 2022 Dominic Masters
+// 
+// This software is released under the MIT License.
+// https://opensource.org/licenses/MIT
+
+#pragma once
+#include "time/ITimeManager.hpp"
+
+namespace Dawn {
+  class TimeManager : public ITimeManager {
+    public:
+      TimeManager();
+      int64_t getTimestamp() override;
+  };
+}