"..he is granted the authority to "operate" the company for a limited time---what is limited when dealing with the FDA?"
You're right, we have no way of knowing the "end" of the FDA process. But as I said, present indications are that the end of '18 might be the target for approval.
If the deadline for sale is pushed off till that specific date, Dec. 31, '18, then there is a limit to the trustee's stewardship, and the distinct possibility of a more robust bidding process.
Plus, the option of a Ch. 11 restructuring might be a lot more attractive to a potential investor.