For the individual levels, you do not have to clear your save file or do anything of the sorts to your existing save file.

Your records are mostly based on the Speed Trial factor but it's your timing that will guarantee you a record.

Most importantly, you will need to start the timer at the same time you "Press Space to Start" You will end the timer when you hit the final beat. You may re-time as needed although I find it simple to map the split button to a key that's nearby the button you usually use to play.

It seems redundant to include a real timer, considering almost all runs of the same speed factor will all be considered the same, however the main point of the Level Leaderboard is to showcase those who can Pass or Pure Perfect songs at higher speeds.

Happy Speedrunning!