Originally Posted by ISP James
if its a gas, they will have you out in no time...
usually a decision is made in the first 10 minutes or less... at least if you're potential or not an option. so if you clear 15-20 minutes and its still moving along well.... your chances are good
I have had long and short interviews, all with different results. The best way to tell is eye contact and facial expression. Don't just look at them, observe how they are acting, etc. Basically, the same things you do when you are bored/uninterested, they will do as well.