It varies.  My 2 Directors don't really require personal assistance.  I usually try and see them at least twice a day.  However since I am on a different floor I also communicate via phone and email.  Very often when I pop down to see them they have others in their office as it's an open door policy.  Neither are interested in scheduling regular meetings with me.

As for the Chairman he is usually only in the office 2-3 days a week at most.  When he does call in, it could be for anything from 5 mins to a couple of hours, depending on his workload and diary commitments.  I communicate with him via phone and text, but he's a difficult one as he is busy with other committees and outside bodies.

That said I find the latter easier to work with for some reason.