As a person who wrote code for a year every day working on a game in my free time, you'd be surprised how much progress you make even if only putting in a bit of time every day. Or maybe you wouldn't be surprised. After all, 365 days * 0.5 hours / (40 hour/week work week) = 4.5 work weeks. So about a month of "full time work" that you would never have if you didn't invest in that half hour daily. Pretty neat. Good way to master a skill in your free time even if you're one of those people that says "I don't have time."
After completing the 365 day streak I even did a little informal "AMA" on reddit where me and some other people suggested their tips on staying productive when coding every day: (https://www.reddit.com/r/gamedev/comments/37i77h/ive_been_wr...)