I have done the FTP Progressions twice. In both cases, in subsequent weeks.
I have found that in addition to doing a new FF or HM, trying to do 3x15 or 2x20 might be better. Depending on the type of riding you do, or want to do, being able to hold that FTP power for longer is just as important as increasing it.
The reason for this is that not every rider’s 20 minute power is a pure aerobic effort. For a large fraction of riders, there is a large anaerobic component to their 20 min effort so they cannot hold their “FTP power” for an hour.