The moment a staff profile is created, via Admin > Personnel > Staff > (Add New), the individual will appear in all staff reports.
You may still create a profile in readiness for their arrival, but are then advised to make the profile inactive so it doesn't show in reports. On the profile, click on the cog next to their name, which will open up their Personal Details area. At the base of the page under the Active dropdown, select No. Then click on Submit to save.
When the staff member starts employment with the school you can make the profile active by reversing the above process, as well as provide them a logon. If you go to Admin > Personnel > Staff, you will find the inactive staff members at the base of the staff list.