Before Lucky's CCL injury (and surgery), we trained off and on for several hours a day.
It was probably actually a little too much...he usually started getting bored towards the end, and I should have stopped before he got bored. We would usually train tricks for a couple sessions of 10-15 min. or so each per day, and run agility for about 25 minutes or so total (including any time it took me to adjust the course, warm him up for about 5-10 min. (should have done more of a warm-up), run him a few times, reward/treat/play for a few minutes, and cool down/get a drink for a minute or two).
Now, Lucky and I are in the post-op rehab stage, so our training is mostly tricks that help him build muscle (sit pretty, SLOW circles, stand-sit, SLOW heeling, etc.), and lasts about 4 or 5 min., and we train 3 times a day or so.
Once Lucky and I are back at agility (fingers crossed), we'll probably train tricks for about 20 min. or so per day, and run agility for only a couple seconds (with a 10 or 15 minute warm-up) twice a week or so, so I don't over stress him.
And, of course, right now we're conditioning for about 20 min. a day with walking/trotting on the flat and walking up hills, and it's going to gradually become more and more.
Great to hear about how much everyone else trains! Sorry to rant so long!