Soo i thougth about speedrunning this game after not playing it for 2 whole years and idk when the igt actually need to start. can someone say when does it need to start?

If you're doing a full game run, your final IGT time will be displayed on the file select under the save file you picked. If you are doing a single chapter run, once you complete the chapter, quit out as soon as the next one starts and the moderators will estimate from there