> Assume there's a reasonable amount of work you need to do to fulfill the base expectations for your job (i.e. your Normal Work) and then there's a little time left over.

In my experience "a little time left over" is usually not enough time to bring meaningful "extra" work to the table. If I'm going to bring in something new and useful, and also be able to sell it to my team, then it's hours of research, testing, and convincing.