There's a glitch in the game that has yet to be patched which causes the white timer at the bottom right to start later than it should. It should start as the starting door opens, but if you look at the timer on the current first place damage% run, it actually starts just under two seconds AFTER the door already opened. The gray timer splits that appear at saferooms are accurate though, it's just the big white speedrun timer that starts late.

I knew there was something weird with the in-game timer