well a quick google search for "intranet timetable software" comes up with a few.
Sorry i think i phrased my last entry wrong "There are some 3rd party" i mean that there is more than likely 3rd party apps.
I have never actually used anything as i feel comfortable buidling my own, but im certain these would fullfill what your looking for but may be too complex to customise to have a simple interface.

This is one of them cases where it may require a developer to implement a system catered for you which you or another then could update/tweak and edit.

If you head about doing this your self then the two bullet points you listed

* Visitors expected at school today (including their picture)
* List of senior management team on site today

shouldnt be difficult to implement and is probably easiest to start with.
But you will then need a back end for staff to edit these details.

Perhaps its best for you to attempt a mock up system for one of these elements and see how far you get. The learning curve is huge but if you break it down you should be able to achieve everything you require. And everyone on daniweb would be happy to help with problems you come across. (Just not particularly writing it for you)


I spose this post has mixed you up even more. Sorry about that.