How much time of your work time you spend for unrelated to your job activities?

50-60%. I'm an intern though.

Depends on what you consider job activities.

In the broadest classification, I spend 0% of the time I'm at work on unrelated activities, because even when there isn't active work to be done, I'm expected to be here in case any other developers need to ask ?'s. Waiting is part of the game.

If you use a more realistic definition - work activities are those related to the active development of software - then I probably spend about 20-30% of my time doing things that are unrelated.