[mdfk]

I don't cheat myself anymore that I can be productive after normal working hours.

My body doesn't want to sit any longer than it already does. And it isn't healthy either. Also mind is not as flexible.

Possible solution for any body issues might be frequent exercise and for mind -- working in the morning as suggested in other comments.

I'm working on my project for around 6-7 months already. First couple of months of work was done mostly during weekends and after hours. But recently I had a 2 week Christmas break which I used to work on my side project full-time. This made me realise how much more productive and creative I'm when I can single-focus on one thing for couple of days in the row. I've redesigned my whole app, it looks and works much better. So in result, a little over one week of work had similar effect to 6 months of working after hours.

So perhaps a good solution is just to take days off to focus entirely on your product and use your after hours and weekends to actually rest.