I use a cheap toy[1] I got for my kid, who got tired of it. It stays next to my keyboard and I doodle drawing exercises whenever I get tired of typing.
A minute here, a minute there, and next thing I know I've completed quite a few of the exercises (about 30m/day, if all the individual minutes are added up).
Works very well, and enforces drawing from the shoulder and not the wrist.
[1] The one I bought (about $10) is this: https://www.takealot.com/kids-digital-12-inch-drawing-tablet...
>https://www.youtube.com/watch?v=eaif0PpNMas&list=PLQ9CsVTcIG...
i did some of my most productive studying on the bus or in hospital waiting rooms. even with a fulltime job i would say that 5-6 hours of drawing in a day is very achievable without much sacrifice. you don't need to be that serious about it, but you probably have more time than you think.