This game seems to me like it's a game where you try to last as long as you can right?
If so this is what I would do:
In your first scene put the following:

In your gameover behavior do this:

In your gameplay scene put this:

Of course make sure you still keep your score drawn where you'd like. What the following does is at first it loads any save data when you start your game.
Next when you enter your gameplay scene if your time hasn't already been reset to 0 it will set your time to 0.
When your game ends if your time is greater than your high score it sets your highscore to time. You don't want to reset your highscore to 0 but keep your time to it's value that's silly.
Let me know if the following works.
Tweak how you'd like! But keep the gist of it.