The timer starts on the "begin" button for the custom game, ends upon entering the sleeping pod.

is in the only run before I came, so that sounds good. there should probably also be 100% but eh.

What would a 100% entail?

all people survive, or all days perfect, or beating it twice to get the true ending. Also some rules on the timings for when you start and end days 2,3, and 4 would be good.

emmm,excuse me,i'm a noob ,and my english is bad,i want to know the stopwatch where can i download

https://livesplit.org/downloads/ there are tutorials on the website and youtube for how to set up