Yeah, 9pm is fine. If there's a group of you it'll probably take a few hours for your meal anyway by which time the rest of the place (i.e the bar areas) will be fairly busy. I've never really seen it too crowded there (which is good) except for the restaurant will no doubt be full. And if you're a meat eater, the steaks there are fantastic.
Cheers mate - had steaks there 4 or 5 times and they've always been REALLY good. Dunno whether it was the Argentinian one or not, but they are always really tender fillet steaks cooked to perfection. 8)