exceptions days in calendar

Hi,

My client wants to define exceptions days in calendar and any PM work orders are not created by run the generate PM work order request in those days. But system allows creating work orders. Please let me know how can resolve this issue? it’s very important for my client for example they have 15 days overhaul time which is not regular and wants to determine these 15 days in calendar as exceptions days and should be OFF that’s why  system should not allowed to create PM work orders in these days and shift them next 15 days from their last