Well, I'm not sure about validating idea. I just used the idea that was already validated by others.
My daily schedule was like:
Variant A:
- 8 AM to 11 AM work in a cafe on my side project
- 12PM - 8PM work at full-time job at office
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Variant B:
- 10AM - 6PM work on fulltime job at office
- 7PM - 11PM work on side project in a cafe, then go home
So actually I was able to get 3-4 hours for side project either in the mornings or in the evenings.
Plus, of course, the weekends were dedicated to the side project too.
Regarding validation, as I said, I didn't validate my idea, because the idea was already validated by others.
Pros: you know people need this Cons: a lot of competitors