I have always had a 'proper' job as well as being a writer. Although in my own mind most of them were part-time to keep the rent and food coming in.
Baker, postman, showman, working on the belt at Nintendo shoving games in boxes, and all sorts of short term things to earn a bob or two. All these jobs also offered excellent 'people watching' opportunities, thus providing a wonderful pool of raw material to work with. Something an 'Ivory Tower' writer wouldn't have ;-).
But I always found time to write, and you tend to become quite good at making the most of opportunities and time. You learn to write to order, to turn on the creative juices almost as soon as you sit down to type. In truth, often before, as you'll find yourself planning a scene or whatever on your way home from work. You also sometimes find you've totally lost yourself in your writing and the night has passed and it's time to go and do your bread and butter job again.
Eventually this will take a toll on your health. I got to my fifties before the cracks started to show, but I'm still paying for it now.
Now I'm retired and I'll admit that having a regular pension has taken some of the urgency from the need to earn extra. My two girls are independent, and someone else is taking care of my ex-wife.
My day to day needs are modest, but my characters won't let me slack off too much ;-)
Gyppo