What does stop time period mean in hockey?

Answer 1

In recreational hockey, many games are played under a curfew. In order to get the game done in time, sometimes it is played with a running clock (meaning, the clock does not stop for whistles).

Stop time periods just refers to the clock stopping for whistles. Some games use a combination depending on the score of the game or time of the game. For example, my local rec league uses running time for the entire game except for if the score differential is less than 5 in the last 5 minutes of the game. This helps ensure the game will finish in the hour time slot.