Allotment Setup

I need to set up an allotment that has points in the plan for new hires how they get their prorate first month worth of hours. The example is below:

• If the employee starts between 1st-10th they get the whole month for the allotment.
• If the employee starts between 11th- 20th they get half of the month allotment.
• If the employee starts between 20th - 31st they get no allotment for the first month.

Does anyone have the plan set up like this?

Has anyone set up employee groups for PTO for certain positions?