Totally depends on amenities on the boat. If you have a fully canvassed boat and auxiliary heat (espar/etc.) then all year round is comfortable. If you have an open helm, you're going to want to stick to late June through early September. We boat in both our 42' Meridian (fully enclosed, Espar heat) year round, and on the Maxum 2800 (fully enclosed, red dot heat while under way, electric heat at the dock) year round as well.
Boating blog: https://highwind.fun/
2008 Endeavour TrawlerCat 48 - Cruising the Great Loop
Used to own: 1999 Maxum 2800 SCR - Serenity - 7.4L/B3