But how about a little later in the year when it's a bit warmer?
As you know, it's connected to BookCrossing Day.
Up to now it has been, and I know there has been previous push back to have conventions around the anniversary of when the site was set up. When the founders came to the conventions it was nice to have the connection to the date, but that hasn’t happened for a very long time. conventions are organised by volunteers and have had no formal support. If volunteers want to create a convention during their countries spring/summer than there is no rule stating they can not.