Thank you for your comment!
But I didn't count the time... I can say that the below things.
- I bought pico-8 on 2019/1/25, and soon start making this game.
- Development was suspended for about 5 months
- The activities after March 2019 are roughly as shown in the image.
I did first try to make a small game as much as possible. But it's became bigger and bigger. haha...