BPM Simulation

Hi all:
I have to simulate a process where the process schedule has to be limited to only work times. I mean, the use case is:

  • A group of employees receives requests from customers to sell products and for every request they start a sale process.
  • The employees work from 9 AM to 6 PM (standard shift)
  • The requests are received only from 9 AM to 6 PM

When I try to simulate it, I can manage the resources availability but I do not know how to schedule the process instances to start only from 9 AM to 6 PM which is the situation in the real world.
Any help?