My guess is that Q primarily meant "think countdown" (the holds not being as important as the "example of countdown from a NASA webpage" context)
And secondarily the hold concept may have meant "don't take the apparent timing too literally, T-0 is not necessarily at the time you'd expect if you simply add the time on the countdown clock to the present time."
That is, NASA planned holds may = unspecified offset between visual clock and real events due to Q obfuscating the real T-0 (not giving away too many details)
Side thought - on classified DOD shuttle flights, we were told that a countdown had started, and the time it started from, but NOT the length of the planned holds, so as to obfuscate the planned launch time. The countdown clock was only revealed during the final countdown (like the last 9 minutes, iirc)
So there may be a connection between holds and not revealing in advance exactly when T-) will happen.