Sometimes "restricted by restaurant" comes up, sometimes not.

I tend to always make reservations for 7:30, because that's usually when we're ready for dinner.

And, that way, if we're hungry earlier we can almost always be seated earlier. If we've had a late lunch or find something interesting to do, it's never been a problem to change the reservation for after 8:30.

Another nice thing about Open Table is special requests. Whenever I've requested a window table, or a particular room, or the patio, etc., we've always been accomodated.