I'm seeing a disappointing lack in "lateral thinking" in any of the answers so far, despite the puzzle's tag plainly telling us that the correct answer will require us to think outside the box, so I'm just going to put this here.
The duration of your vacation was:
This is because:
You are God, and after setting off the Big Bang you decided to take a well-deserved vacation. From the time of the Big Bang, it took nine billion years for the Earth to form and have an atmosphere which was then capable of being either clear or cloudy.
Nine billion years is 3,285,000,000,000 days. The remaining 18 days cover the final few days of your vacation, during which there could finally be weather for you to enjoy (as derived in all the other answers)
I hope your vacation was a restful one, O Lord!