No, the countdown for both start at the moment they are ordered. After A was ordered, the countdown started. When B was ordered, then it has its own countdown but they are running at the same time.
You can go to your “My Gigs” section, find your gig and set a maximum for how many orders are in your queue.
If you get order C tonight, it will be running at the same time as the other orders.
Best (don’t read too much on the forum, sounds like you have work to do…)
NOTE: If you are sure you can’t do them both, you need to request an extension from one of the buyers as soon as possible. They may decide to cancel and that’s not ideal if you are new, but you can ask (Use the “Resolve Now” button on the second order, request an extra day or two…)