If your organization provides different amounts of PTO to part-time vs full-time employees, you can create different PTO policies for each group.
Go to Settings > Paid Time Off.
Create one policy with the applicable rules and PTO amounts for your full-time people.
Create a second policy with the applicable rules and PTO amounts for your part-time people.
Click the arrow next to each policy name and choose the Assign Policy menu item to configure the list of employees who have access to each policy.