Just started on this game over the weekend, didn't have a ton of time to play yet. I hate the calendar thing. Time limits in games always make me nervous because it puts me into the mindset of "I have to play optimally". I'm trying to resist it, but I do have a question. I just opened up the ability to ask people to join my class and recruit them. When I fail to recruit, I get a notification of what they require stat-wise to join up. If someone says "Axe and Riding" does that mean total units in my class with axe and riding skill, or Byleth's specific Axe and Riding skill? It was kinda unclear. I hope I don't have to raise a bunch of skills on Byleth just to recruit the people I want.
Aside from the side stories, there aren't really any time limits.
Yes there is a story battle you have to do each month, but you don't get to choose when to do it, or whether to do it.
You have four options to choose how you spend your weekend, but you never want to choose rest or lectures. Those are really only there if you don't actually feel like battling or walking around the monastery.
Of the remaining two options, you should always be choosing monastery. The only times I would say battle are if you have battle quests/side stories that you want to do, or if you have absolutely no money etc and want to grind. Even then, I would say to wait until you have two battle actions (can battle twice) before doing it.
To sum it up, monastery>battle>>>>>>>>the other two.
Later in the game you will have more action points at the monastery than you know what to do with.
On my second playthrough I would just spend many weekends resting because I have nothing else worthwhile to do, and want to continue with the story.