Going through the speedrun categories, I haven't found any runs that used a Nintendo Switch. Is this because of the timer on screen rule? Or is it because it's slower than all the other platforms?

Speaking of the timer on screen rule, are we able to edit a timer in after the run? For example, I would record the run, then time it in "post."

Consoles are generally slower and harder to use than pc, so nearly everyone does pc. A few people have done switch I believe though.

For the timer, it depends on how you're capturing the recording. If you're recording on a pc with a capture card, then having a timer is relatively easy to do. If you're playing on a tv/handheld mode using a phone to record the screen, don't worry about the timer.

Generally for timers, if you're able to do it you should. So anyone recording on a pc should have a timer (i think ps4/5 has an option to do it too).

I have a stone age mac that I usually record my runs via capture card. Because I have a mac, I usually use FramePerfect on my phone to time.

As far as I’m aware switch has the slowest load times and completely different RNG than all the other versions, making it (extra) difficult to get a competitive time. That being said you should run the game on whatever you’re most comfortable with and swap to PC if you ever find the opportunity and the motivation to make the switch (pun intended)