Some comments about countdown holds …
The usually stated rationale for a "hold" is to provide quiet periods when people can catch up on any work that is running behind schedule. It would seem simpler to simply run a countdown straight through with blocks of time (say, a few hours) without much on the schedule to allow catch-up on tasks behind schedule - if you know the duration of a planned hold, why not just not have a hold?
In practice I saw two reasons for this.
First, on RARE occasions, a planned hold was shortened (for example, when it became apparent that weather would be a problem at the planned T-0 and there was no hard reason why flying a little earlier than planned would be a problem.) This was extremely rare, I don't know that it ever happened with shuttle, it may have been some small unmanned rocket.
Second, and more important for shuttle, much of the countdown worked the same way every time, there was a regular schedule for what happened at T-6 hours on the clock, etc. Sometimes the "launch window" (period of time when the shuttle could fly while meeting all objectives and requirements) was short, sometimes long. It would be short for a rendezvous in space, long for a flight that didn't have such precise requirements.
The shuttle had a max period of time it could hold near launch, due to astronaut fatigue laying on their backs in the crew cabin. So when there was a short launch window, NASA would plan a longer than normal hold close to launch – which if looked at backwards meant getting ready to fly earlier than necessary, and then sitting back and waiting until the Earth as in the right place for flight. Sensible strategy.
Likely not too relevant, since we don't think Q has done this dozens of times before, and adapted a familiar countdown clock to a new situation. But since we're looking for patterns in the meanings of holds, might be useful.