Calculate the time it takes to enter/exit play mode in Unity editor

BenchmarkEnterPlayMode.cs

using UnityEditor;
using UnityEngine;

public class BenchmarkEnterPlayMode
{
	[InitializeOnLoadMethod]
	private static void Initialize()
	{
		void OnPlayModeStateChanged( PlayModeStateChange state )
		{
			if( state == PlayModeStateChange.ExitingEditMode || state == PlayModeStateChange.ExitingPlayMode )
				SessionState.SetFloat( "state_exit_time", (float) EditorApplication.timeSinceStartup );
			else
				Debug.Log( state + " in: " + ( (float) EditorApplication.timeSinceStartup - SessionState.GetFloat( "state_exit_time", 0f ) ) );
		}

		EditorApplication.playModeStateChanged -= OnPlayModeStateChanged;
		EditorApplication.playModeStateChanged += OnPlayModeStateChanged;
	}
}

How To

Simply create a folder called Editor inside your Project window and add this script inside it. Now, every time you enter/exit play mode in the editor, a message will be logged to the Console, showing how long it took to enter/exit play mode.

This is mostly useful to quickly benchmark the effectiveness of different Configurable Enter Play Mode options: https://docs.unity3d.com/Manual/ConfigurableEnterPlayMode.html