The OOTB Operator unavailability is recording only dates and not datetimes and there may be chances that the user/operator is not available on a particular day from 3pm to a particular day 11 am. So the assignments need to be routed to different users based on the datetime instead just date in these scenarios and the Pega OOTB operator unavailability is not supporting it. Would like to submit it as an enhancement or feedback request to implement this feature in future releases by Pega so others may get benefit at some point, if there is no any alternative option available to achieve this requirement. If we need to modify the OOTB properties to datetime by creating new datetime props then we have to update at many places and some of the rules are final so we feel if Pega do the change then it would be more secure and efficient approach.
As mentioned above, there is an enhancement request (FDBK-29677) submitted for this query. You could request your Pega Account Executive to connect with the Product management teams to know the progress on the request. Use the FDBK-29677 as the reference id.