Software Update Menu Bar
SUMB is a companion app for scheduled macOS updates via Declarative Device Management (DDM). Featuring a live menu bar countdown, it gives end users continuous, subtle visibility so they can plan their reboot on their own terms, avoiding abrupt disruptions during critical tasks or meetings.
Readme
Just download and install the .pkg, no configuration needed. Once a scheduled DDM update is deployed from your MDM, the menu bar icon will display the time remaining.