As you can see from this video, the framerate seriously impacts the in-game timer. The upper left video completes the race with an in-game time of 3:53 and an RTA time of 4:07. The lower right video gets an in-game time of 3:54 and an RTA time of 4:23. The FPS in the upper left video likely averages around 100 or so while the lower right video averages around 210 or so.

Timing begins when "go" appears in the center of the screen and ends when the race is finished. Runners are not required to have a timer of any kind displayed in the video. Moderators can and will retime races when necessary.