The advice given in this thread is good. Based on my time in the navy.
Your limiter should be time. The recommended ship crew (technical) should spend half of their work day time in preventive maintenance tasks.  Work days on ship are normally 10-12 hours. If they try to squeeze in more personal development, that normally comes out of the personal time and PM time, they should not get more than 4 hours normally on personal development. This doubles the learning new skills time as that is based on 8 hours per day study (at least in the older editions).

The Superyacht discussed the other day was going in for it’s 5 year overhaul which will take 6 month. So expecting an annual overhaul to be 1 month puts it on par with modern shipping. Annual maintenance is the perfect time for crew vacations, you don’t want them to go stir crazy.

Charles