Yeah, taking on this kind of challenging, continuous-learning work is fun... but it's generally only sustainable as long as the total time you put in to both "education" and "work" doesn't exceed full-time.
Trying to negotiate that up-front, though, is hard. Most employers don't like paying much for education and research, and they don't like people who want to work less than full-time, either.
It's tricky. If you have an intelligent employer, they will understand that as a professional, learning is as much part of your job as fixing bugs. If your employer is not intelligent like that, but the company isn't a sweatshop, you probably might be able to "slow down" your ticket crunching a little bit in order to get some directly relevant learning in[0] (that, over time, will actually improve your work results). If your job is a sweatshop, be happy that in this industry it's still relatively easy to change jobs.
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[0] - not saying use your job time to learn CV-padding stuff; just if you suddenly need to work on a codebase in a language you don't know, don't be afraid to read an actual book instead of minimal amount of StackOverflow answers needed to kill your fist ticket.
Trying to negotiate that up-front, though, is hard. Most employers don't like paying much for education and research, and they don't like people who want to work less than full-time, either.