How Do I Start A Speedrun Timer To Speed Run The Game?

just do for example classic obby, record the run and submit it, u dont have to worry about the time since mods retime it

Yeah just use the ingame one. The mods retime it don't worry about it. Other games may vary depending what game you play. If you speedrun doors for example you would need it but speed running Pet Simulator it already has a timer.