Safranbolu is pleasant in most seasons, but the old town is at its best in spring (April-May) and autumn (September-October), when the temperatures are mild, the light is good for photography, and the crowds are manageable. Summer brings heat and more visitors, particularly on weekends when day-trippers arrive from Ankara.
The saffron crocus blooms in October, usually the first two weeks of the month — the purple flowers appear briefly in the fields around the valley, and the harvest (before 8am, when the flowers are still closed) is a remarkable sight if you can arrange to see it. Winter is cold and occasionally snowy, which actually suits the stone and tile of the old town well, but some guesthouses and restaurants reduce their hours or close.