How long does it take a nonpoisonous snake to kill something bigger than it?

It depends what it's constricting. As an example, some of the first snakes I had would only take live food. Average kill time for a rat (from seizure of the prey to death) was around 15 seconds by one of my Royal Pythons. A full-grown Burmese python I helped confiscate from an 'idiot' - was eating live rabbits (until I managed to coax it onto dead prey). It would take around 45 seconds from seizing the prey to death.