?..when 1 skien isn't quite enough

I knit a hat and it ended up being too small, so I frogged it and am starting over with more co’s. The hat that I frogged used up almost all of 1 skien so I know that this hat will use a little more than 1 skien. My question is this…should I knit until the first skien is gone,even though it will be nearing the completion of my hat, and then start using the second skien or should I knit the hat about half way and then switch to the second skien? Or doesn’t it really matter that much? :??

Doesn’t matter. However, if the start of the new skein might fall in an area where it’s difficult to join new yarn (if the hat has a lacy area, for instance), I’d start the new one where the join will be the least obvious.