When a leave application is entered into ESS, the hours calculated will be based on the workdays and hours in the Employee's Work Planner. Any days that occur within the leave period and are included in the Public Holiday planner that is linked to the Employee's Location will be excluded from the calculation.
If there are other days that need to be excluded but aren't included in the Public Holiday Planner, then the employee enters multiple leave applications and splits the leave to exclude those days. Examples could include, if the employee worked during the leave period, a company shut down period (e.g. over Christmas) or school holidays for employees in the education sector.
Likewise, you can't prevent employees from applying for leave on particular days. For example, if you have a Leave Block Out period during your busy time where employees can't take leave, you can't block employee from applying for leave during this period. Managers or Approvers would need to Decline any leave applications that occur in this period if they don't want the employees to take leave.