7 days counting the first day of use. So if you use them on Sunday, the last day you can use them is on Saturday. This 7 day expiration applies even if you only use them once or 10 times in the 7 days.
As phamton posted, "7 days counting the first day of use. So if you use them on Sunday, the last day you can use them is on Saturday. This 7 day expiration applies even if you only use them once or 10 times in the 7 days"