I'd prefer there to be a 24-hour waiting period, with the "commissioner" option. I would hope there wouldn't be a need to veto any trades in this league, but it feels messy to have a separate poll for each trade when 24 hours allows people the time to contact the commissioner if there is a problem.
If the unlikely happened and a trade was vetoed, what do we do about the stats that were accumulated in the meantime? No, I think a 24-hour waiting period is reasonable for a trade to be processed, and keeps things simple.
My 2 cents