You'll know when and if the yeast start taking off by color change and by smell. when you first pitch it will smell malty and worty, once the yeast dig in it will smell bready and yeasty. If a few days go by and there is no color change/smell difference then you probably have some bum yeast.
Stepped it up once and now if I put an air lock on it for a while it starts bubbling. Very surprised it's alive after over a year in the back of the ice box. Looks like I brew tomorrow.