If we get there on the 930, do we have to leave on the 230? Or can we stay till the 5 o clock departure

Leave at 9am or 12 noon. it's an hour to the island, and return at 2:30 or 5pm, your choice.

boats leave from Gulfport ar 9am and 12 noon, you can return from ship island at 230pm or 5pm, your choice! Ship Island Excursions

Yes

Better have lots of sunscreen though. That sun is rough out there