FAQ03179 of Counters FAQ

Time Counters measure time and display the amount of time that has been measured. They are also called total time meters or hour meters. Hours is not the only unit available, however, and time can displayed in minutes, seconds, or in some cases even days.
Time Counters are not Timers. You set a specific time with Timers and an electrical signal is output when that time has elapsed. With Time Counters on the other hand, you do not set a time. They simply total the time and display that total. If you were to define the two in terms of timers, then Timers would be Preset Timers and Timer Counters would be Total Timers. Time Counters, however, have historically been classified as Counters.