I wonder what these dates actually point to? When a company was founded could mean so many things.

The summer can be a great time to develop and plan. If you're raising funding, from what I hear, the worst times are July-August and Dec. People take holidays, etc and you want to be timed for that.

But that doesn't mean you're not working? Build your product, get test users, etc. etc. Now is always the best time.