For now, setting up compensatory or comp time is not supported in QuickBooks Online. You can only track regular and sick vacation in the program. Let me share this article for additional details about this: Set Up and Track Time Off in Payroll.
Feel free to submit a feature request about this to our product engineers. Your feedback is incredibly valuable and is directed to our Product Development team, assisting us in enhancing your experience with QBO. Check out this article on how to share your feedback to them: How Do I Submit Feedback?.
I'd also like to give you these resources in case you need more information and guidance when tracking time off in QBO: