This question already has an answer here:
As a software developer on a relatively small team handling a big job, I have never found myself with no tasks on my plate; new work comes frequently, and completed tasks are quickly replaced with new ones. However, I will occasionally find myself with short periods of time (think fifteen minutes to an hour) where I don't have any work to do. There can be a handful of reasons for this (code is compiling, I'm waiting on other people to do things, etc). Part of me says I should enjoy the downtime, but if there are several instances of it in a week I start to feel like maybe I'm not working hard enough.
What is the best way to deal with these very short periods of not having work to do?