Marmaris is a Mediterranean summer town. The season runs roughly May to October, with the heat peaking in July and August (regularly 35°C and humid). The most pleasant weather is in the shoulder months — late May, June, and September — when the sea is warm, the days are long, the worst crowds are not yet there or already gone, and prices are noticeably lower than at peak.
Winter is mild but very quiet. Many hotels and restaurants close from November to March, the boat trips stop, and the Bar Street neon goes dark. If you want Marmaris-the-town with a beach feel, do not come outside the high season.
The Marmaris International Yacht Festival in early May launches the sailing year and is the best moment to see the gulets all in port together. Ramadan dates shift each year — Marmaris is liberal enough that most restaurants and bars stay open as usual, but worth checking before you book.