The best time to visit Mahdishar is late spring through early autumn (May–September). Summer temperatures here are genuinely mild — the 1,630-metre elevation keeps things cool even when the Iranian plateau is baking — and the mountain terrain is at its greenest. This is also when the nearby Shahmirzad summer resort reaches its liveliest, and when the Parvar Protected Area offers the best conditions for wildlife watching.
Winter brings heavy snowfall and cold temperatures. The Alborz passes can close intermittently, and access to Darband Cave may be difficult in deep winter. Spring is the next best option: the snow is melting, the valleys are lush, and if you time it right, you may catch the early stages of the Sangesari nomads' spring migration.
Avoid visiting during the peak of Nowruz (Persian New Year, around 20 March) unless you enjoy crowds — Shahmirzad fills up with domestic tourists during the holiday week and accommodation becomes scarce.