I think a set schedule/routine forces you to get "in the zone." You can veer off sometimes based on what else is going on in your life, but I feel like a schedule is still good.

If you take a day or two off from a diet, you're more likely to quit the diet altogether. If you don't practice your instrument for a day or two, you're more likely to get rusty as you continue to rationalize skipping days. Weekends are normal in most work environments, but I wouldn't get too creative with your schedule.

I like the idea of two hour bursts followed by a break, as many have a hard time concentrating for more than a couple hours at a time. For coding specifically, this seems to make sense. With my job, I have to continue to keep tabs on certain ad campaigns all day long, so this schedule wouldn't make sense. I think it could be ideal for you. Try it out and adjust as necessary!