This is the amount of time, in minutes, billing records can sit queued without reaching the count threshold, cdx6500NMNPCbillThresh, before the node places a call anyway to have them printed. This is the time-based backstop to the count-based threshold; on a low-traffic node that might never accumulate enough billing records to hit the count threshold, this timer ensures records still get delivered periodically rather than sitting indefinitely. For example, a timer set to 60 minutes on a lightly-used branch node ensures billing records get printed at least once an hour even if traffic is too light to ever hit the record-count threshold.