All the good programmers I know have side projects and live and breathe code. None of the mediocre/bad ones I know do.
Think of it this way: what's likely to make you a better programmer: spending half (0.5x) of every day on (a work-mandated subset of) code or spending most (1x) of every day on code? The answer is obviously the latter.
And it sounds weird, but most of my programming knowledge comes from outside of work, even the knowledge that I apply at work. Maybe it's because work naturally discourages exploration since you're focused on the company's priorities. For example, I'm never implementing a collection in C at work (I use `std::vector` and stuff). Yet doing that in my own time taught me why certain operations invalidate iterators -- a thing senior coworkers of mine didn't understand and which helped us catch a bug. :D