My immediate assumption was that it was fixed. It certainly seems a bit convenient that the only housemate of the 15 whose absurdly early eviction could widely be deemed amusing and entertaining without causing any real backlash was the one who actually got evicted. As soon as they started hinting one of them would be going, I was thinking "right, well, surely they've got to fix this so that it's Simon, right?".
But I don't know how, and I don't quite go with this thread's tack of "IT'S ALL FAKE THEY'RE ALL ACTORS NOTHING'S REAL BLOODY HELEN SOMETHING SOMETHING WAKE UP SHEEPLE". Is it possible the contents of the "timebombs" could be modified live, some kind of mechanic that would allow for that? It would be a bit of a convoluted way to achieve not very much, especially with all the nonsense about being able to swap bombs with Adjoa.
I'd have no problem with it being a fix, to be clear. It's not like there's a legal issue, any phone votes or anything. If I was on the production team and the decision had been made to have a launch night eviction, I'd bloody well make sure it was fixed. The alternative is that they just survived what had a 93.333% chance of being the most pointlessly self-defeating twist in the show's history out of dumb luck.