Hello Dron231! Thank you for the feedback!
I agree with you that we should be able to play individual levels as they are not really linked (you do not keep your speed between levels, unlike Celeste for example). As a matter of fact, this is clearly something we have to add to the game.
About the timer mechanic you suggest, I find that it could lower the barrier of entry to the speedrunning aspect of the game. And I truly love it! However, we should keep two timers: one with the restarts and another one without the restarts. So players managing to complete all the levels without any restarts are rewarded!
PS : Thank you for the bug report! We will investigate this one.