May, June, and September are the sweet spot — the lagoon is warm enough to swim, the town is busy enough to feel alive without being overrun, and the restaurants are all open. July and August are the local high season; Moroccan families from Casablanca and Marrakech fill the place out and accommodation is at a premium. October through April is quiet, with cooler water, fewer restaurants open, and a flat-grey Atlantic atmosphere that is rather pleasant if that is what you came for.
Oysters are best in the cooler months — September through April — when the lagoon temperature drops. They are served year-round but the texture and flavour are markedly better outside of midsummer.