You can order from the full menu at the lounge. But you must check in at the second floor desk and they will only let you up to the restaurant if there is room in the lounge for you. (The bar and lounge area is small. At the beginning of the night it will be taken up by those waiting for seating on their ADRs, but if you just hang around at the bar until they start seating you can get a chair and table in the lounge)
They don't start serving food until 5:30 but they will serve you a drink while you wait if you go up to the lounge before that.
There is limited counter seating where they make the sushi but I think people book those. You can ask at the desk if they have a seat available there. If they don't just ask to go up to the lounge.