Most software engineering professionals spend some part of their at work time studying. Many also spend additional personal hours at it.
There's no perfect metric - some jobs will be slow enough that you can spend whole days studying between work task assignments. Others will be so busy that you won't have much time beyond the immediate research focused on "what's the right way to do the thing I'm trying to do right now???"
Estimation
As you say - the assignments come first - and it's always worth it to get a sense for how fast you are expected to get something done. When estimating a task - do provide a buffer for the unknown in a given task, but don't pad time for open ended research that doesn't relate to the task. However, if you need to learn something to do the work, plan on the time spent learning as part of the work. That time shouldn't be huge, or there's a real skills gap between the expected skills of the job and your skills - but I'm not surprised if in a 2 weeks task, an engineer occasionally needs 2 days to learn new stuff... depending on the work.
Daily learning
Another metric I've respected is that many of my colleagues spend 1 hour a day learning something new in engineering that's not necessarily directly connected to their regular work. Things like new languages, new messaging protocols, new design patterns, new things in networking, new security vulnerabilities - stuff that fits into closing the inevitable hole of "we didn't know what we didn't know". The tough part is that almost no one I know works as specific number of hours - so some days it's 7 hours, some days it's 10... and they end up fitting in the learning around the long hours. I do think that the time box of 1 hour is particularly good - it makes you focus on something, without getting totally lost in it. It gets you through some depth, but not so much that you know everything about a topic - it makes a good index that may trigger a memory right when you need it.
More than an hour to spare?
If you've ended up with more than an hour a day to spare for learning, you're in a rare position. My impression and personal experience is that the industry is pretty hot and the need for engineers is so urgent that most are paid well and given high expectations on delivery. Most are expected to learn very quickly and to be constantly improving in efficiency with new tools and processes whenever possible.
If you have the time - great... but if it seems like you can spend the majority of the day, most days, learning - you may want to check in with your manager on whether your rate of efficiency is what's expected.
