This can be done both within the Staff module or within the Time-Off module. Below find the instructions for the Time-Off Module. (Staff option can be found here)
*Substitute Managers -
If the Substitute Managers
option has been enabled for this account, leaving the Email box unchecked for a Manager will make them a Substitute Manager. These Managers will only receive an email notification for a time-off request when all main Managers are away on that particular day.
Managers can also be assigned by the Import/Update by CSV function in Staf