The system is designed to not enable users to book holiday on the same day as a public holiday in the system.
The public holiday will deduct from their entitlement if this option is selected in their planner settings, or will be seen as a non-working day for them.
If you have public holidays set to deduct entitlement you can edit the duration of this if it's not displaying the correct value for this day.
📌Note: The duration of any entry added over a bank holiday will not be taken into account.