I currently school D in 20-25mins max, so for her, I'd school her. As she's still learning everything, I don't generally do the old 'warm up' as such, she'll get her 5-10 mins of walk before we up the pace into trot where we tend to do a few nice circles, Serpentines and changes of rein etc. As part of her warm up, we tend to incorporate leg yields and shoulder fore (she's pretty flexible for a 3yo!!!) to loosen her off and 'get her on side'. If we miss out the leg yields then I tend to find we fall out thru our right shoulder on left circles as we return to the track a lot more.
As a cool down I tend to do about 3-5mins, of walking, halting and some changes of rein etc. I'll generally add canter in literally at the end before I cool down for a couple of goes on each rein. I could really do with taking her in the field to solidify her canter now as it's come on enough to do more than just 1 side of the menage but it's an uphill menage and she has been fairly trippy when unbalanced so I'm reluctant to start cantering her downhill just yet! We will trot downhill but it's a constant check, release, check, release to keep her from running (that's when she trips as she just plows onto the forehand).
So yes, a normal schooling session on D.
Gem, probably some trec training. I'd try and focus on one to two obstacles or our CoP however, and again, 5 min warm up and less of a cool down as if I'm practicing obstacles it tends to be fairly slow going anyway (a lot are done out of walk).