Hiya - got to say, I'd really like this! I find if I start with short poses, all it does is get me frustrated and I don't start to relax until I do some longer ones - I then do much better on the short poses after I've warmed up with the long ones :-) My IRL life classes have started experimenting with this too and it's been great so far: this week we did 3 x 5/6 min, then 5 x 2/3 min, then a few 20-25 mins to finish. It felt really helpful as the initial not-too-short poses gave enough time to ease in gently without getting too fussy, then the shorter ones pushed the analytical brain further out of the loop leaving me able to relax in the longer poses. I'd love to be able to just choose a 'set' of pose lengths for a custom class - could also help to guard against what sometimes happens when I have it in same-length mode and just leave it running: I get distracted and forget to go to bed...
