AAARGH, connection error. I had a (IMHO) really good and long awnser for you, but then a connection error!
So here's the shorter version, wich I'll copy-paste first before posting again
Assuming you want to have a constructive training session in wich you can consolidate severel skills, take 20-30 minutes.
For me a quick spinning session would look something like this:
5 minutes of warming-up and active stretching. Focussing on the wrists, elbows and shoulders. A little bit on the back and hips, less on the legs, etc.
Then 15-20 minutes of several individual spinning exercises. Taking time to practice the skill in both your dominant and non-dominant hand. Depending on the skill/exercise you can do between 3 to 10 different ones in the set timeframe.
Then take time for a few minutes of free spinning, combining the trained skills and the movements that just feel good.
End with a few minutes of static stretching, main focus on your wirsts and lower arms
If you want to learn a new skill, same warm-up and cooldown, but take the 20 min. trainingtime for that one single exercise. Don't forget to do some free spinning afterwards, you're body and mind will thank you for that.
If you want a quick form-training session. Same warm-up and cooldown, then about 20 minutes of form-training, anyway you like.
If you want a quick sparring/application training session.... Good luck, we forget time when practicing application and doing some sparring and have never been able to just practice 20 minutes. Just give yourself the time and freedom to have fun.
For me, I get more out a training session if I plan more time then needed. Lets say I have a schedule wich on paper should only take 30 minutes, I plan 45 minutes. It gives me rest, rest in my head, time to take it slower, take time for a specific exercise if my body ask for it, or just have a few minutes of extra time to sit down and do nothing. That way I don't have to rush my training.
I had a lot more to say on this topic, but that's for another time.
Just remember to have fun along the way and enjoy your training sessions.