Due to multiple factors, expect to potentially pay more when booking in December. For low rates, September can be a great choice for travel to Stockton. Flights to Stockton from León, Guanajuato in September are about $608 on average during September, but can be found for as low as $286.
Regardless of the time of day you decide to fly, the ticket price will remain around the same. Book flights from León, Guanajuato to Stockton as you normally would.