The Maintenance Counter counts the total time the Input connector value is 1 and forwards it to the Output connector whenever the Input receives a falling edge on the signal. The unit of measure of the time is defined through the Time UoM property of the node.
If the Reboot survive property of the node is enabled, the counter value is persistent which it means that it doesn't get lost when the server reboots and after the reboot, the counter increments the last saved value; otherwise, the counter value gets resetted every time the server reboots.
The Start Date output connector sends the last date and time the counter received a Reset signal. When the Reset input receives 1, the counter gets resetted, Output goes to 0 and Start Date is updated, the counting will start again only after Reset goes back to 0.

 Behaviour of Maintenance Counter

Behaviour of Maintenance Counter