If you're looking at 3D, have you considered playing around with the tutorials on Unity learn? You make small prototypes during the courses which gives you insight into the software and gaming fundamentals.
It does sound like you're aiming to make a time management game. They are particularly complex in terms of how many things must work together and work separately at the same time. It's a difficult game for a starter game. Games like point and click adventure games - where people simply walk around and click things - or games with simple game play like Sokoban / space invaders are easier to make the first time round.
There's nothing wrong with making a complex game first, but you need a lot of motivation to keep going because as you say, it will take months before you can play it - and with starter games - there's normally many bugs which specifically are things that you did not foresee happening, and therefore did not provide code to cope with it due to a lack of experience.
When I started I set myself a goal of creating 10 small games - at least 30 minutes each, each one had different game play and graphics features, before attempting a full length game to gain the knowledge on coding and game play. That way I was creating a playable game much faster which kept me motivated. It also meant that I had own examples of most features that I was going to put into a larger game.
Tip: Play a lot of games in the genre you're writing. That is the best way to know if what you're doing is fun or tedious. Avoid the aspects of those other games that you find annoying, and keep the aspects that you find fun.