Hockey games are played in three periods. Each period run for 20 minutes. However some games may be played for 15 to twenty minutes depending on the level being played.But three periods,each of the same amount of time are standard.
Games that are tied at the end of three periods go into overtime which run for five minutes in the regular season, but it changes to a 20-minute sudden-death style in the playoffs.
There are two fifteen minute intermissions in between the play periods.If the game is tied at the end of three periods in the regular season, it is followed by a 5 minute overtime and then a shootout.
Whereas, in the playoffs if the game is tied at the end of regulation additional periods with intermissions in between will be added until someone scores, which immediately ends the game.
Why does hockey have periods and not halves or quarters like most other games?
Hockey has three periods to create an opportunity of an unfair advantage for one team on purpose.