I heard from one of my friends to avoid making a reservation at the Uffizi when the tours/tour busses arrive. Apparently there's some time when they’re "allowed" or large groups are more frequent. Has anyone heard of this before and if so, what time do they show up? My current idea is to make our reservation towards noon to get out of the heat, but I can reconsider if necessary.
Tour groups show up all day and are not limited to certain hours.
I would suggest making your reservation when the museum opens at 9 AM. Being one of the first ones in means no previous groups are lingering. It doesn't mean there won't be any, but some morning walking tours end at a museum so the tourists can stay longer if they choose. If it's a morning walking tour, it will end around noon in the museum.