If not setting a condition, then will run indefinitely until power drained or machine broken.
TimeStamp could be started from zero according to Epoch's definition. It is legal. But AMI, Award, ARM Bootloaders usually defines the timestamp (must be measured in 1000 ticks) starting from product released year, which the default number could be very outstanding (It must not be zero, it looks like "1455260975"). I think the OS is designed to be bricked if user has set something outstanding.