I've experienced their manual approval delays on opening orders (when I was above my overnight holding limit but, of course, still below my daytrading buying power limit), up to a minute and a half. The worst was when I put in a market order - it was uncancellable while it was undergoing manual approval.
It's odd that they manually approve closing orders, too. Seems like a waste of their (and your) time.
When I talked to them about this a couple years ago, one option discussed was to open and account with, and move money to, their Cybertrader division. The rep said that Cybertrader was understaffed compared to them and likely didn't do as much manual review of orders. I decided not to move at the time because Cybertrader charged a high monthly fee for their software unless one did a level of trading that was larger than what I was doing.