One concern I have with a few hours a week is unless the project is really really tiny, you can begin to think that it'll never get done and it fizzles into nothingness.
For example let's say you want to make X app and it takes you 2 full time months to go from an empty folder to shipping an MVP. Let's just call it 300 hours. But if you only put in 5 hours a week (about 1 hour a day) it will take you 60 weeks to finish it. That's over a year of chipping away on something which is a very long time. You'll probably drop it well before you finish it because it'll feel like it's dragging along forever.