Short workdays for specific period

Summary:

We need to create a shorter workdays for a specific period only for Elapsed employees.

Content (please ensure you mask any confidential information):

We have elapsed work schedule of 9 work hours a day.

For coming holidays period we need to create a shorter workdays of 8 work hours only for 2 specific dates.

When tried to add an exception in the work schedule it requires us to define start and end dates and hours. But as we are defining this for elapsed work schedule the start time and end time are not relevant.

Any suggestions how to create such exceptional days with shorter work time for elapsed employees?