New customer Duo order question

I’m coming from AT&T and planning to switch to T-Mobile tomorrow morning. Once preorders go live, will the Duo be available as a device option right away when signing up as a new customer? I’m hoping to trade in my current iPhone toward the Duo and use T-Mobile’s offer to help pay off the remaining balance on my AT&T phone. Basically, I want to know if I can open my account and place my Duo preorder immediately when preorders launch, or if there could be a delay before it becomes available to new customers. I planned to go to Costco in person tomorrow to have a rep help with this but curious if I can avoid that all together