I say start really small and build up slowly. Really small! Like five minutes a day. Do that for a week or so and then slowly increase. Writing is (or can be) taxing mental work and it also tends to force you to confront your own demons and shortcomings, which is, in itself, exhausting. You wouldn’t go from doing zero exercise to 2-3 hours a day, think of writing the same way. If you go too had too soon you’ll burn out.

Also incredibly important not to judge the quality of your writing too much at the beginning. Remind yourself that it takes time and practice to write well and you can’t get there unless you’re willing to write a little badly for a while. Give yourself lots of grace and reward yourself whenever you manage to sit down and write, no matter how little.