Love Annecy, so much to do in the area.
We’ve been 5 times as a family group, 3 times in August and twice in October.
The Summer months are extremely busy and hot. October was way better with a nice temperature and not as crowded. Didn’t really find that places were closed because it was October. Maybe May would be the same.
Some excellent walks in the area and the bile ride around the lake is really good especially on a tandem.
Chamonix is well worth a trip for a ride up one of the cable cars or the train, just be prepared to empty your wallet for the experience.
edit @toby1 we had a similar experience after doing the walk of Mont Veyrier. So much so that any bout of tummy troubles from then on is known as Annecy Anoos!