Gerry G
Ovens are not always preheated before using. Crock pots are never preheated.
Diane B.
They're generally used un-preheated but I always let mine heat up at least a bit before adding the ingredients just to help bring everything up to temperature more quickly.
Sometimes too, some of the foods being added to the slow cooker are sauted first (perhaps onions, for example) or just heated up a bit first, again just to bring *everything* (crock and food) up to full temp sooner (for safety or for shorter cooking times).
ckngbbbls
I have never timed a crock pot that closely. You don't need to either. That kind of cooking is different than baking.
Sharon S
The time starts when you turn it on. They have no way to preheat them.
?
Crock pots aren't' meant to be preheated. They're meant to put cold things in, and it heats up gradually to cook a long time at a low heat