When to make your one rebuy?

[Kristian]

Playing at a local casino, I participated in a MTT with buy-in 200$ with one rebuy of 133$ (strange $-amounts calculated from local currency). Same amount of chips are bought with the rebuy as with the buy-in.

I will always rebuy unless I get lucky and make a big stack early, and the extra rebuy chips won't have a significant impact on my stack. Is this thinking correct?

Second question is, when is the best time to make this rebuy? Should it be made as soon as someone makes a bigger stack than mine (which most times will be after only a few hands), or should I wait till my stack is so short I have lost the potential of aquiring a really big stack?

Any comment is welcome, thanks in advance.