I work 40h/w as a janitor, which includes heavy lifting and lots of running between floors to change lightbulbs et cetera.
I have two, long running, comics going on as well as creating short comics in the mean time.
However, I only dedicate 3-5 days a week on making comics, allowing myself having 5-6h/day (and getting 6h sleep) on those days.
(Monday, Wednesday, Friday/Sunday are my webcomic art days, the rest are personal art or short comics! Personal art can also be a warm up as well!)
Start slow. Allow yourself to take time making dinner and such if you're living alone (like me) with no pets and make sure you sleep and eat well.
Some weeks I work on my comics all week, allowing myself to take a week off.
Experiment and see what fits you and your needs. Take a day off making dinner, like lots of them. You'll save money and time by taking that to work and eat at home as well! I mean, 3 minutes to microwave your food vs 45 minutes making it daily?
One thing that's worth mentioning is that: Sit down and draw, start with warming up drawings, whether it be headshots or something else. Do this for an hour or so, depending on how much time you've got and then (either eat or) start drawing on your comic.
But try to draw a little every day, it doesn't matter how much it is, as long as it's a little something. If you're having a bad art day, walk away and do something else.
I struggle ALOT with my performance anxiety, and some days I just can't art at all. I feel terrible about when I'm not at the drawing table. However, it's very much needed. "Me"-time should always be considered.