I think its some sort of rugby
There are three periods in a hockey game.
There are three 20 minute periods in a regulation NHL game.
Playing a video game about sports.
There are three (3) 20 minute periods.
Three (3) twenty minute periods.
There are three 20 minute periods.
Three periods of 20 minutes!
You can not! It's a game you keep on playing!
Three 20-minute periods.