Generally, a QT tank is not to have live rock in it so no need to "cycle". Live rock will absorb any medications that you may need to place in it should that QT become a HT. You can have a permanently running tank with a HOB ready for animals or a stand-by that you will fill with tank water. Your choice. Once you have a specimen or specimens you need to control for ammonia. Your HOB with a simple sponge filter and a bottle of bacteria is a good way to go or just regularly test for ammonia and perform necessary water changes. This is where the "set up a few days prior" comes in. Alternately, you can have a fish or two always in there but then you will have to remove them before quarantining the new arrivals. This can be stressful for those fish that have happily made the QT tank their home and now are dumped into the DT. If your new arrivals will need to be medicated, then you have the fish that have always been in there now needing to be medicated as well, if you did not take them out and place in you DT.
A read, in case you missed it... because your QT might very well become a HT and it is applicable in both situations, more or less.
https://www.reef2reef.com/threads/ammonia-control-in-a-hospital-tank.296119/