I just took a second to think about how I'd use an apprentice's time over the fifteen years of their apprenticeship.
Certainly it would change depending upon the particular magus and the particular apprentice but I'd like some feedback on my choices and how you see it differently
You've got 15 years* 4 seasons per year so a total of 60 seasons;
You spend 15 of these seasons teaching your apprentice so you've got 45 left to get some work out of them.
Right almost from the get go they can start copying laboratory texts (artes Liberales 1 and Latin 4(appropriate specialization)), because they can do this at very little cost to you and because down the line you'll want to load up on texts for big projects that take advantage of you apprentice's score in the last few years of their training I'd imagine that it's not uncommon for the apprentice to make copies of both sides of a deal where lab texts are traded. That is they copy the lab text(s) of their master to trade to another magus and they copy the lab text(s) of that magus that the master receives during the trade. I'm thinking 10 seasons that leaves us 35
Fixing Arcane connections: They'll need a lab and they'll need to have their arts opened but once again the barrier to entry is fairly small. I can easily see magi having their apprentice get some practice in by fixing connections for their sodales. If the magus is spending a season in the library this seems like a good choice. I'm thinking perhaps 8 season that leaves us 27
Extracting vis: When the apprentice gets a bit of experience under his or her belt this will probably be the go to activity for the apprentice during the seasons when the magus isn't in his laboratory. I'm pegging it at 12 seasons this leaves us 15
Adventures: With or without the magus along apprentices are too useful as magicians not to be used in that capacity at least a bit, I'm thinking one trip every three years so five seasons leaving us 10.
Laboratory assistant: This is the most stereotypical activity but also the hardest one to get just right. I think that most magi upon starting to train an apprentice also start designing three or four spells or items that will really benefit from the extra few points that an apprentice brings to the lab at the end of apprenticeship. These projects could be what the apprentice was extracting all of the vis for. I'm thinking that two projects at three seasons and two projects at two seasons is about right. So 10 seasons using up all of the 15 years worth of time.
To sum up, I see a typical breakdown of a 60 season apprenticeship as follows:
10 lab texts (edit : and casting tablets)
12 vis extraction
10 lab assistant
How do you see it? What activities have I missed?