Start with the geography, because it decides almost everything about a couple's weekend here. Hilton Head's twelve miles of developed beach face east and southeast, out at the open Atlantic. That means the island gives you sunrise over water and takes sunsets somewhere else: over Calibogue Sound, over Skull Creek, over the marsh grass on the Broad Creek side. Couples who plan a romantic evening on the ocean beach and then watch the light drain out behind them have made the single most common mistake on the island. Sunrise is the ocean event. Sunset belongs to the west side, and you need a boat, a dock or a west-facing table to get it properly.
The second thing to understand is the pace. There are no high-rises, no neon and no strip. The building-height and sign ordinances have held since the 1970s, which is why the island reads as a forest with a beach attached rather than a resort town. Nightlife is thin and closes early by design. What the island does offer instead is unusually good at the quiet end: 60-odd miles of leisure trails to ride at first light, a Forest Preserve that is essentially empty at 8am, a dozen beach accesses where you can walk a mile without passing anyone in March, and water on three sides with resident bottlenose dolphins in all of it.
Timing matters more than budget. March through May and September through October give the best weather-to-crowd ratio: warm enough for the water, quiet enough that Coligny is walkable. Mid-April is the exception: the RBC Heritage takes over Harbour Town Golf Links and rates across the island go up with it. High summer is hot, humid and busy, and the sound-side sunset cruises sell out days ahead. Oyster season runs roughly October to April, which is the argument for a late-autumn trip that most visitors never hear.
Below: where to actually watch the sun go down, why a private charter is often cheaper than it sounds once you're splitting it two ways, which beaches stay quiet, what Harbour Town becomes after the day-trippers drive out, the twenty-minute run to Old Town Bluffton for dinner, and how to spend a night on Daufuskie where there are no bridges and almost no cars.