You can find a tutorial on FNAF: Security Breach Speedrunning discord server. I dunno if it is illegal to post links here, but here's the invite: https://discord.com/invite/sbspeedrunning. When u join, go to resources channel and go to the very top. U will find the tutorial there. edit: oh wait, i thought u meant u want to stop timer as soon as u finish the game, the was an easier option. u could just press RMB on the livesplit and then click on 'edit layout'. Then press + and add a new timer. double click on the new timer and change timing method to 'Game Time'. That way u get 2 timers, one for real time and second for game time

Have you tried using autospliter? You can download it on resources page