I recommend the PB fitness eBook.
It advises no more than three "Lift Heavy Things" sessions each week, one of which can be very short. The key is intensity---not necessarily time or number of reps.
You should start dips, chin-ups and pull-ups using less-intense alternatives---e.g. do assisted pull-ups until you can do 50 reps then progress until you can perform unassisted pull-ups. See Mark's progression videos on youtube.
Form is important, do a less intense exercise if you can't maintain good form.