When did the crack in Amy's wall re-open?

Question

One of the major character background elements for Amy Pond's during her time as companion was the fact that she grew up with a crack in the universe in her bedroom wall. This forms the key plot element of the first series with Matt Smith. Eventually, this crack in her wall closes in "The Big Bang" as a result of

The Doctor sacrificing himself and allowing himself to be absorbed into the crack

at which point we see it seal itself off.

However, about 10 minutes into "The Eleventh Hour", The Doctor closes the crack in Amy's wall by forcing it open, then allowing it to shut. He even explicitly points out "See, I told you it would close, good as new." as we see it appear to seal shut in the same manner as "The Big Bang".

The scene in "The Eleventh Hour" happens just before The Doctor leaves Amelia Pond waiting in her garden for him to return; the scene in "The Big Bang" happens just after Amelia falls asleep in the garden, waiting for The Doctor.

So what caused the crack to re-open in that short interval?

Answer 1

While at little Amy's bedside, The Doctor says "The cracks can't close properly until I'm on the other side." I'm guessing that in The Eleventh hour, that crack hadn't closed all the way. It did, when The Doctor finally gives in. Also, there's an entire time-stream being re-written here, as the later events of The eleventh hour have never happened now.

Answer 2

The Doctor doesn't go through the crack in Amy's wall. He uses the exploding TARDIS to send the particles that are inside The Pandorica

(the ones that revived this Dalek)

to every space and time at once. Thereby, using the explosion to rewrite everything back to the way it is supposed to be. However doing this trapped the Doctor inside the explosion which was sealed off by him repairing it.