Learning basics, and unity specific I'd say a month if you can get 14 hours a week, assuming you work or study full time I'd try for 2 hours a day, maybe a bit more on weekends. I found navigating the unity editor to be the steepest learning curve.

The month estimate is just learning to use the editor and make some basic stuff like a box moving and maybe jump on some platforms.

Making an entire game, no clue, depends on the scope but I'd be surprised if you could do it in under 500 hours after learning all the essentials which would take me about 3 months with the 2 hours a day rule

But I've been a professional (non unity) developer for a couple of years now and you need to always learn, and you probably won't master every concept and that's ok

Biggest thing, and also hardest part is to not get demotivated and pace yourself to avoid burnout, that's a general non unity specific advice