If the couples rest the same amount every hour, and you know that they rest for 25minutes in 5 hours, you can use cross multiplication to determine the amount of time they will rest in 8 hours:
5hours____25minutes
8hours____x minutes:
This means that the rate of the resting time and the hours is the same. To determine how much x is, multiply 25/5 by 8
After 8 hours the couple will dance for 40 minutes.