Of course, you can draw with the mouse. If you just use the doodle board on the internet, you can also draw the effect with the mouse (some foreign countries can't). But if you use drawing software, the mouse has no pressure sensing function, and many boards can't draw the effect of the mouse. For example, if you only have a pencil, it is difficult to draw the effect of a brush.
If you want to draw well, it is not how long you draw, but how much you draw. They also study painting. Some people become painters in their twenties, while others are not yet forty. Those who work hard must draw better than those who don't.
There are many bookstores that offer introductory animation courses. However, for traditional art, it is still recommended to sign up for classes (not the online "animation school", but the kind of studio). Having a teacher's guidance is completely different from self-study.
The time to draw a picture depends on the author. If you are talking about computer painting, it usually takes several hours to dozens of hours (I am a snail, and I have no foundation for dozens of hours, haha).