usually 50-100 degrees too low. it will ruin your cookies to bake them at the incorrect temperature. my oven is also calibrated incorrectly. i have to turn it to 385 degrees for it to actually be 375 degrees.
if they cook faster than 8 minutes the oven is too hot or the cookies are too small. if they take longer than 10 minutes the oven is too cool or the cookies are too big.
it is important to wait this 2 minutes. they continue to cook from the heat of the sheet without being over-cooked in the oven. also, they will hold together better and be less likely to fall in the 