I have been trying to get one of my villagers to master 3 areas for some time. Actually I have several that I have been training on other things. I started out with a fairly young villager that had mastered a task and then switched to another task to try and master it. How long does it take or is this a you never know kind of thing. This is the only puzzle I have left. I have already started VV3 and hope something happens between the games.

There are several factors at work, including the job the villager is working on and the villager's individual makeup. I've explained how learning works more thoroughly in this answer in our Support FAQ.