The best place I have found for checking dates is under the hunting tab, "harvest reports". Click on the species you re interested in, and go to the bottom of the page, and you will see the dates for every hunt for that species, followed by Unit boundary descriptions.
As I recall, Wyoming will announce the starting date for each hunt in the big game proclamation, but does not set the actual season length until after the deadline has passed for entering the controlled hunt draw. Same is true of permit numbers. However, in watching a number of hunts for multiple species, it appears they rarely change the season length from one year to the next.
Scoutdog