Unity 6000.3 toolbar Time Scale slider with a reset button.

ToolbarTimeScale.cs

using UnityEditor;
using UnityEditor.Toolbars;
using UnityEngine;

namespace Nadaked.Editor.Toolbar
{
    public static class ToolbarTimeScale
    {
        private const string ResetElementId = "Nadaked/TimeScaleReset";
        private const string SliderElementId = "Nadaked/TimeScaleSlider";

        private const float DefaultTimeScale = 1f;
        private const float MinTimeScale = 0f;
        private const float MaxTimeScale = 5f;

        [MainToolbarElement(ResetElementId, defaultDockPosition = MainToolbarDockPosition.Middle)]
        public static MainToolbarElement CreateResetButton()
        {
            var icon = EditorGUIUtility.IconContent("Refresh").image as Texture2D;
            var content = new MainToolbarContent(icon, "Reset Time Scale");

            return new MainToolbarButton(content, ResetTimeScale);
        }

        [MainToolbarElement(SliderElementId, defaultDockPosition = MainToolbarDockPosition.Middle)]
        public static MainToolbarElement CreateSlider()
        {
            var content = new MainToolbarContent(
                "Time Scale",
                "Change the game time scale");

            return new MainToolbarSlider(
                content,
                Time.timeScale,
                MinTimeScale,
                MaxTimeScale,
                OnValueChanged)
            {
                populateContextMenu = menu =>
                {
                    menu.AppendAction("Reset", _ => ResetTimeScale());
                }
            };
        }

        private static void OnValueChanged(float value)
        {
            Time.timeScale = value;
        }

        private static void ResetTimeScale()
        {
            Time.timeScale = DefaultTimeScale;
            MainToolbar.Refresh(SliderElementId);
        }
    }
}