It was the whole season. Claire didn't spend too much time with Nathan as I recall, but what if Nathan had decided to take her to Mexico for another impromptu vacation? Would Noah or Angela have told her not to go? And what reason would they have given?
Or would they have simply gone on blindly trusting that Matt's brainwashing would work properly? Angela at least was having doubts.
The whole scheme was stupid and poorly planned. They needed to be a lot more desperate, in order to excuse it. There needed to be a plotline leading up to it in which the metahumans were known to be public enemies and were being hunted down more seriously than they were. There should have been legislation pending to send them all away or some such, public sentiment is divided, it's a make or break moment, Nathan's in Congress trying to block this insanity and then WHAMMO Nathan gets killed by an insane metahuman. If that becomes public knowledge, it all goes straight to hell. Angela, Noah and Matt needed to have their backs to the wall a lot worse than they did.