I think that a few hours a week is at least enough time to maintain a hairpiece.
This week, I've been pretty lazy, and have spent a total of maybe 20 minutes re-gluing the hairline (I'm using tape at the back which has lasted me about two weeks this time, though I'll be redoing it soon). I should have probably spent a bit more and re-glued once more earlier in the week, but was busy and just wore a hat until I had the time.
It's not that hard to maintain, once you get the hang of it. Of course I still have to spend a bit of time each morning styling my hair, but that was true with my own hair as well.
It's definitely not for everyone, but for some it's a valid option. I'm only 22, and had pretty severe hairloss that I just wasn't happy with. For me, the hairpiece has been a good thing, though it can be VERY trying at times when I'm having trouble with maintenance (there's a learning curve, but it was worth it for me).