Cattolica is built around the summer beach season, which runs reliably from May to mid-September. The peak is mid-July to mid-August, when most Italian families take their ferie and the resort is full — beaches packed, restaurants on waiting lists, prices noticeably higher. June and September are the sweet spot: warm sea (24°C+ in September), reliably hot weather, but distinctly fewer crowds and significantly cheaper hotels.
Outside the beach season the town largely shuts down. Most hotels, beach concessions and seafront restaurants close from October to April, although a small year-round core stays open for the resident population. Spring and autumn weekends can be lovely for a walk on the empty beach.
Note the timing of two festivals: the Festival of Flowers in late May (which officially opens the season) and Mystfest — Cattolica's International Festival of Mystery — at the end of June.