Sorry for this amateur question...

But, if the over/under was 2.5 rounds, and the fight ended in the middle of the 3rd round... Is that an over or under?

Fight must go 2 full rounds and 2 min 30 sec into the 3rd.  If it ends 2 min 31 it is under.  2 min 29 it is over.

@spl1t

Exactly how he said only viceversa

2.31 is over, 2.29 is under if it ends 2.30 exactly don't know what it means, maybe a push on your bet.

@realdeal52

 I think he is meaning the time left on the block. If there’s 2 min 31 seconds left, it goes under. 

@Skanless1

 Time left on CLOCK not block 

@realdeal52

 It's a push happened to me before