We're trying out DAP to see if it will help calm our dog. We have the
dispenser that plugs into an AC outlet. My question is does the
dispenser need to be plugged in continuously to be effective, or can it
be plugged in just during the time the dog is alone? The unit didn't
come with much documentation and it's not clear how long it takes to
start emitting the pheromones. TIA

It needs to be plugged in all the time. Some people have found DAP
collars to be more effective.
Depending on the problem , DAP might not be enough on its own.
Alison

We've heard about the collars, but couldn't find them on eBay. Do you know
where they can be purchased?