Maybe I'm missing something here, but I never really thought about it that hard - there were times, even in grade school and middle school (and certainly in High School) where I was playing much more than an hour a day. The year I was a freshman in high school, I was always playing because that's what I lived for. I'd go to the band room 30 minutes before first period band class so that I could play and warm up. Then I played the band rehearsal. Then, immediately after lunch I'd head up to the band room and play until jazz band or show choir started (they alternated days and I was in both) so on days I had jazz band I was playing more. Then, after school I'd head to the band room and play some more - probably 30-40 minute worth - before I went home. THEN, I would either take my trumpet home and practice that evening, or I'd come back to the school after dinner to play in pep band, which consisted of two sessions - one pre-game session, and then the halftime session.

I made more progress as a player that school year than I have ever made in such a short period of time, and believe me, I was SLAMMING my chops. I used all kinds of excessive pressure and shamelessly used the "octave key" - especially during pep bands when I was playing as loud and hard as I possibly could.

So am I a freak? I don't think so. I think that the chops can be pushed pretty hard and it won't kill them or do a lot of damage unless way too much mouthpiece pressure is an issue - I was always able to get past the pressure thing by blowing a lot of air, but I put the horn to my face on more than one morning after a pep band where my lips hurt a bit and I had abrasions in the insides of my lips where my teeth dug in. The thing is, I didn't have anyone there telling me that I wasn't doing things right. I continued to improve by leaps and bounds that year, so I figured I must be doing something right. (Disclaimer - I developed a lot of bad habits during that time too, some of which plague me to this day)

I say to go for it and don't think about the clock so much - if it winds up being too much, THEN back off.