You can if there is room. The later in the evening it gets, the more the lounge becomes a place for diners to wait for their tables and it's very very difficult to get a seat in there. If the place is that full, they will not allow you elevator access. There's just no way of knowing how the crowds will be on any particular evening. If you have been there before, you know how small the lounge area is.
The last THREE times we've gone up early (and they let us up early) there wasn't a seat to be had in the lounge or at the bar. We had to grab a couple of stray chairs and prop ourselves up against the back wall, out of the way.
The lounge is always full when we dine there. If your lucky you might be able to grab a few chairs. We always walk outside on the observation deck when we are waiting for our table.