There is no single or easy answer to your question. I can only share my experience. I used to steal time from my routine to ensure that I get at least couple of hours a day on average (which, if not sufficient, is adequate) on working day and some more time on weekends. For example while I lived in Navi Mumbai and used to commute to Dadar (by train around 45 minutes), Instead of travelling by train (where one hardly gets place to stand), I preferred to travel by bus which used to take around half an hour more than train commute. So, I had to start half an hour early and reach home half an hour late. But then, I get clear 2 hours which I used to work on the “investing part”, my secondary profession. Similarly, Since, I had 5 days a week, I generally devoted 5-6 hours to Investing on Saturday and the rest of the weekend was all family time. To be honest, it was not easy and took some time for the family to accept it. However, once they realized that this was my passion and I was eventually aiming to make my “secondary” profession the primary one, and I was working towards it, they supported me whole heartedly.
I know many of VPers like Ankit, Kiran and many more who devote sufficient time to this, despite their full time job (and demanding they are at times!) and come out with some excellent scutllebutt and analysis. So, it boils down to where there is a will there will be a way!
Having said that, being full time also means that one has to accept some limitations such as one may not be able to travel at will for management interactions and/or AGM due to leave constraints or work load/priorities. One may also have to be selective in “short-listing” ideas to dig them deeper as compared to full time Investors who may have more time at their disposal and hence can experiment more and be digging deeper more number of ideas.