StarMaster:
Unless and until someone comes up with a better system
I do not quite follow why not just stick to the suggestion in MGT RAW.
With the ruling in place it's incredibly easy to acquire new skills.
Compare with your career terms.
If you rolled really lucky you get perhaps one skill per year (1 for Service, 1 for Advancement, 1 based on Events, 1 based on Mustering Out).
MGT RAW states (and actually fumbles the example ^^):
([current skill rank] + [new skill rank]) weeks
Also, it states that
Jack Of All Trades cannot be learned
Further, there's the delicate matter of what is actually downtime.
It's not quite as if there is absolutely nothing to do during a jump, certainly not for a Steward who needs to pamper the passengers.
So, I would rather suggest to count a jump week as half a week of possible Training.
Just my 50 pence ^^
Physical Training
Strength 3->4
4 weeks (or 7 weeks per my suggestion)
Intellectual Studies
Streetwise 2->3
3 weeks (or 5 weeks per my suggestion)