And yes i'm comparing against in-game time

Thank you for your answer Jonah but i found the problem! I was not using the "vault" save but "load 00" so livesplit didn't understand that i begin to 53:01 (the "start timer at" don't change anything. Have a good day!

It happens only if i click on "activate" in edit splits

I have a weird problem with live split, in fact when I reset the timer with NumPad 3 it sets timer at 0:00 and not at 53:01. Please help me, I would be very grateful !