But I'm not aware of the administrative details, or who makes the final decision.

Actually, telescope time on all professional scopes is highly booked and prioritized by a network of bureaucratic committees. Every time some supernova or other sudden event demands telescope time, somebody's research program is usually set back. In most cases, this is just an inconvenience, but in some it could really be a career-killer.

Complex decisions involving the importance, time-criticality and repeatability of an observation must be made, and I suppose mistakes and disputes are common. It must be a lot like being on the organ transplant waiting list.