How do you set up the speedrun timer? I'm planning to make a speedrun but edit it with my phone.

Try looking at part 8 here: https://www.speedrun.com/speedrunning/thread/pt010#ch8How_do_I_time_my_runs_ Generally though, you just need to record some footage of google's stopwatch and edit that over your run on mobile. I don't know of anything that can be sideloaded (other than maybe on android, but I have 0 experience with android phones)