How long before the first puppy is born when labor begins?

Anywhere from a few hours to a full day.

Here's a link detailing the stages of labor and delivery in dogs, well worth a read.

Stages Of Canine Labor - When Your Dog Gives Birth (http://www.2ndchance.info/caninelaborstages.htm)

It almost always happens in a few hours to a day and a couple of hours when your dog gives birth make shour u help her wit the pups if needed.

It depends, some pop them out one after another, others have one, clean it up before they have the next. I had a chihuahua have a pup then had another 18 hrs. later. Really

IT DEPENDS, SOME POP THEM OUT ONE AFTER ANOTHER, OTHERS HAVE ONE, CLEAN IT UP BEFORE THEY HAVE THE NEXT. I HAD A CHIHUAHUA HAVE A PUP THEN HAD ANOTHER 18 HRS. LATER. REALLY

Then you were extremely lucky, any more than 2 hours between pups and you should see a vet. Dogs are not like cats who give birth over a day or two, dogs do things much faster and by waiting your risk major complications.