Fireworks nights change the whole island's evening. During HarbourFest, Shelter Cove Harbour runs fireworks on Tuesday nights from roughly early June to the middle of August, plus the Fourth of July. Parking at Shelter Cove fills long before the show, the surrounding roads back up, and boats on the water charge accordingly. Check the current season's schedule before you build a night around it, and arrive far earlier than feels necessary.
Sunset time is not tour time. The single most common mistake is booking the sunset cruise and arriving at sunset. Boarding typically closes fifteen minutes before departure, and departure can be more than an hour before the sun actually sets.
Evening cancellations happen. Lightning inside a few miles keeps boats at the dock. Operators reschedule or refund for their own cancellations; late arrivals and no-shows are usually not refunded.
The bugs are real at dusk. No-see-ums around the marsh edge in spring and early autumn will find you on the dock. Repellent before boarding, not after.
Alcohol rules are the operator's, and the state's. Bring-your-own is common but not universal, glass is banned everywhere, and the crew can refuse boarding. If you are on a rented boat rather than a crewed one, remember that operating under the influence carries the same consequences on the water as on US-278.