So if i beat my own PB in a category before my first run gets approved, should I delete my own obsolete run or leave it for the mods to mark as obsolete? if a mod could answer that would be great, then I'll know from now on.

thank you.

Just leave it, that's what I do if I get a PB

I’d delete it because if you don’t the mods will have to end up verifying both runs which means more time they have to spend verifying, and, with 80 runs in queue, anything helps to reduce the time needed to verify those runs. However, at the end of the day, it is your choice whether or not to delete it.

Don't delete it if you don't want to. Obsolete runs count towards PB history.