how much time do i have to spend on studies to get the most out

Just balance it out, you learn different things from doing quick studies than long studies. If you are just starting out don't feel bad about spending a lot of time on something simple! Just try to be as thoughtful as you can.
Let's say you are doing basic proportion studies, measure them until they are right, this might take either 10 minutes or an hour, but you learned from it.

To me the most efficient is to do a bunch of quick studies and a few rendered ones. Also drawing from imagination and using references to make it as good as possible helps!

Time is irrelevant, stop thinking about it. Study and do it until you understand. Repeat to turn concscious understanding into subconscious understanding.

>>2745865
It is relevant for some people. I may be homeless soon so I want to learn as much as possible