It really should depend on the role. If part of your job is being available for inbound requests, or participating in group work of some kind, it seems reasonable to expect that during the business day you will be available and not randomly tied up with other commitments. It would be hard to have two such jobs.

If it’s a task completion kind of job then it shouldn’t matter exactly when the tasks get done as long as they get done.

But you should be able to have one “high availablility” job and one “task completion” job at the same time because your tasks can always be set aside if you are needed. Or two task completion jobs, for the same reason.

In all events, the point is being able to perform your job without undue obstacles. If you can do that, and you’re meeting the goals and criteria set for you, nothing else should matter.