Can we learn to adapt to image-reversal when being intermittently exposed to them? I know that human vision can get accustomed to reverse vision when wearing reverse glasses for several days. But does it work when we see the reverse image just in certain moments throughout the day? Would it be easier or more difficult for humans to learn use a reverse mirror?
Wearing prism glasses needs adaptation of behavior. That takes time. Wearing them during all waking hours speeds up the process as it forces the wearer to adapt in everyday life. If the subject does not adapt quickly, it's going to be a very hungry, un-showered, immobile and eventually a very unhappy subject, because tasks of daily living become pretty much impossible without adapting to the prisms. 

Putting them on for an hour or so per day will not force the subject to cope with it. And even if a training regimen is commenced in that hour, when the subject puts them off the learning process stops. Eventually they may get there, but it is certainly not as effective.