When should I visit Santorini, Greece, for the best experience?

The Ephorate of Antiquities of the Cyclades runs the island's sites on a calendar that tapers rather than switching. In the summer season, from 1 April to 31 October, the Akrotiri archaeological site opens Monday and Thursday from 08:30 to 15:30 and on Tuesday, Wednesday and Friday to Sunday from 08:00 to 18:00. Those long days then shorten week by week in autumn: 08:00 to 19:30 from 1 to 15 September, 08:00 to 19:00 from 16 to 30 September, 08:00 to 18:30 from 1 to 15 October and 08:00 to 18:00 from 16 to 31 October. In the winter season, 1 November to 31 March, it runs 08:30 to 15:30 and closes on Tuesdays.

Ancient Thera, on the Mesa Vouno headland, is the site that genuinely rules out parts of the year. In the summer season it opens Monday, Tuesday and Thursday to Sunday from 08:30 to 15:30 and closes on Wednesdays. In March it opens Monday and Thursday to Sunday, closed Tuesday and Wednesday. In November it opens only Friday to Sunday. For December through February the Ephorate's page states the site is closed for the period while also noting it is open by arrangement with the Ephorate — so a winter visit there is a request, not a timetable.

Fixed national closures apply across the island's sites: 1 January, 25 March, Easter Sunday, 1 May, and 25 and 26 December. Greek Orthodox Easter moves year to year, which means one unpredictable spring date is closed regardless of the published weekly pattern.

Akrotiri's excavation is roofed, so its long summer evening hours are usable in a way the island's open sites are not — the Bronze Age streets are walked under shelter while Ancient Thera's hilltop is fully exposed.

The two major archaeological sites close on different days — Akrotiri on Tuesdays in winter, Ancient Thera on Wednesdays in summer — and neither closure is signposted at the other. A two-site day planned for a Wednesday in July delivers Akrotiri and a locked gate; the same plan on a Tuesday in February delivers neither.

• Spring — March opens Ancient Thera on five days a week, and Akrotiri switches to its long summer hours from 1 April.
• September — The single best overlap: Akrotiri running to 19:30 in the first half of the month, Ancient Thera on its full summer pattern.
• Deep winter — Akrotiri at 08:30 to 15:30 with Tuesdays closed, and Ancient Thera effectively by arrangement only.

Length of stay is capped by law, not weather: the European Commission's Schengen rule allows a maximum of 90 days within any 180-day period, and Greece is a Schengen state, so island-hopping plans that run long need counting. On safety, the US Department of State places Greece at Level 1, Exercise Normal Precautions. The real scheduling traps are the two differing weekly closures and the moveable Easter Sunday closure, which lands in a different week each year.

The Santorini things-to-do question in this group gives the admission prices for each of those sites and the island's two archaeological museums.