If it is purely a time thing then position training may be good as it can be done with little preparation - just strip and assume the position. I would suggest some form of timer with an audible alarm so you know how long you have been in that position. Alternatively, memorising the tracktimes on a CD album and using the length of the tracks as a way to work out the times (if you fancy doing quite difficult mental maths while naked on all fours, practising presenting your genitals to your webcam for your Master... I think the task is hard enough without that).

You'll probably only manage 5 minutes at first and that will seem like a lifetime (which is why the music sometimes helps as it takes your mind off the boredom but may defeat the purpose of the exercise) but you can build on that.