A time span is the difference between two dates and times. For example, the time span between 12:00:00 January 1, 2000 and 18:00:00 January 2, 2000 is 30.0 hours. Time spans are measured in positive or negative ticks depending on whether the difference is measured forward or backward. Each tick has a resolution of 0.1 microseconds (= 100 nanoseconds).