The 6 hour transit rule is for award tickets; I don't know of any published fare which has a 6 hour stopover rule. I guess the OP presumed the FF award ticket rules applied to other fare products. They don't (both good and bad). So you have to research the rules carefully before buying, for things that matter to you, and don't assume that all are the same -- surprising amount of variance. Of course FT exists in part due to this.