why is this "Scrum" specific? Sounds like working a 9-5 at most companies regardless of their development process.
Scrum's pre-committed units of work across the team promotes this; its one of the reasons that many groups prefer flow-based methods (which can support regularly-timed releases simply by shipping the features that are ready at the time of the release cutoff) rather than Scrum's cycle-based method.
If there's no slack in your sprint schedule, well there's your problem.
A good manager could think past that, for sure, but I've never encountered a good manager that felt Scrum was good or necessary for their teams.
Then management comes over and asks why you're slacking off.