This was one of the most impressive sights I've seen. You can walk right up to the edge (no railings) and look down towards the water crashing against the cliff. You're up so high, that the seagulls flying down by the water look like fruit flies.
We went to the Empire State Building late at night (maybe 11 or 11:30). We walked down after we saw Jersey Boys. It was perfect because there were no lines....but you could see all the ropes for the queues, and they went on forever!!
I'd spend at least an hour up there. Take photos, grab a drink -- chill out and rest. You have to pay to go up so might as well get your money's worth. Check out all the rooftop pool's while you're there.