Only if you are assigned to an Auxiliary route or holding down a Regular route where the Regular Carrier is out for an extended time AFTER 90 days.
RCAs that only work occasionally or on multiple different routes do not earn Leave.
Designation 78 is an RCA that doesn’t earn leave
Designation 79 is an RCA assigned to an Auxiliary route
Designation 74 is an RCA assigned to a “hold-down”
Your Designation code is the # next to your name on your timesheet (if you’re wondering).