From Onboard Updates (Sept 1):
Check-in time establishes eligibility for non-revenue space available (NRSA) travel on United Express (UAX) flights for United employees.
The policy states that for placement on the Departure Management (DM) list for a UAX flight, the United employee must be ready to travel. Working crewmembers cannot ask for placement on the DM list for UAX flights that are not part of their current NRSA travel. Some crewmembers request placement on the DM list for UAX flights for which they will stand by after they complete their IDs.
Crewmembers also ask stations to place them on the DM list at the
beginning of their domestic IDs even though the UAX flights are later that night. Please remember that check-in time is the accommodations criterion, and UAX will treat all employees equally.
Check-in can only occur when the employee is ready to depart on the UAX flight. This includes NRSA connections, but not those cases where the NRSA travel will begin later in the day and is not part of the inbound NRSA connection.