You can check but most orders can go in at the end of May. Pricing on all models may not be released but they can order the vehicle. Production change over is going on with most models now. By the second week of July most are changed over. Deliveries are from mid August.
Not I said most as with the way things are anymore times can vary on some models.
I had a Great Uncle who was an lead engineer for GM every year and would order two cars every year sight unseen in many cases. So I leaned the drill then and for some reason I always end up buying a car in the summer and have to deal with these times and decide if I want the deal on the past year or the new features of the coming year. I normally go with the better price as the new features on what I am buying are never much.
The GMC was one of the few vehicles I did not buy in July or August.