Honfleur is busy most of the year but truly heaves between July and late August, and on summer weekends — a combination of French families and day-trippers crossing from Le Havre. May, June, and September are the sweet spots: open restaurants, longer daylight, fewer coaches. Winter is quieter and cheaper but many smaller museums and shops close on Tuesdays and reduce hours.
The Fête des Marins (sailors' festival) at Whitsun, which takes the chapel of Notre-Dame-de-Grâce out in procession, is worth timing a visit around. The Festival du Cinéma Russe in late November is another local fixture.