Actually, as i said it is in the OPS (1.1110 2.1) as 168 hours, which equals 7 times 24 hours. That is why it is called a weekly rest time.
There are two weeks on two weeks off contracts over here as well, however you have to have those rest times in between duties. Same as other rest times it is just a normal rest time between duties, just a tad longer than the others.