It takes anywhere between 2 and 3 minutes. 40 seconds seems a bit fast to me, as if you're only nebulizing about 1/2 the medicine.
A problem I noticed with the vials is that if I wasn't careful, sometimes the medicine would get stuck (like behind an air bubble) inside the vial and only come out partially or not at all. I had to tip the vial slowly so that it didn't happen (opposed to just flipping it upside down quickly).
Obviously if you're getting all the medicine in there and it's still taking 40 seconds, then you might just have a really efficient head! But I bet not all the medicine came out of the vial.