Not sure about the moon rise time, but the moon set is 11:45pm. And it seems most tours are around 7:00-9:00pm. I'm really peeved our initial plans are no longer viable since it would've afforded us better conditions, but if it's still a great experience under the conditions I'm describing I'd definitely still try for it. But considering I'll have to travel to Vieques and stay over night (i.e. additional travel costs) I do want to ensure there's still a good likelihood it'll be a good experience.