Outlook 2003 Shared Calendar issue

I share my calendar with about a dozen employees and have authorized them to create appointments for me. The problem is that some of the appointments are being setup for 30 minute timeslots and I would like a minimum of one hour between each one. Plus, some of them are setting up appointments that conflict with other appointments already scheduled.

Is there a way to make it so that the system require appointments to be no less than one hour, and also block appointment creation if it conflicts with other appointments?