Like after a few seconds their game just starts and it syncs perfectly with livesplit

That's because when they load up the game, they'll likely press start either when livesplit says -2.70 or -2.50. Then when the level starts the timer will say 0.00.

But I don't think I understood the question well.

if they have -3.27 on livesplit, and they reset and start livesplit at the same time, then spam the start button, it will be very closely synced.

that was poorly worded