you need to take her temperature (rectal) daily. when she drops to around 98 degrees- she's ready. when you squeeze her teats- does milk come out yet? if so she is very close to delivering.
you need to get her into the vet asap for an exam hon. also- discuss a plan for delivery- do you know how to tie off the umbiblical cords/etc and clean the pups up if the mommy doesn't? ask him to teach you how. Also- be prepared to nurse the pups incase she doesn't- have some pro-biolac or other formula on hand and bottles just in case.
you need to get a plastic kiddy pool and line the very bottom with plastic and newspaper- then make the top layers soft old blankets. keep her in a room like a guest bedroom or bathroom/laundry room where it is quiet. do not let her run loose outside- she needs to be leash walked only. Go ahead and get the #'s /maps for your local after hours vets should an emergency arise during delivery (labs are usually pretty good about birthing though so i think you'll be ok.) The last litter of lab puppies i delivered at the shelter was a litter of 6
all healthy and they had a great momma.
Be sure that you have gloves, scissors, gauze, thread, formula, bottles, a kiddy pool, LOTS of blankets, a heating pad, etc on hand!
Your vet can also give you other suggestions. I'm only a pm away if you need anything hon! I deliver puppies pretty often at our shelter so feel free to ask away if you have a specific question.
Also -does she have any discharge yet? if it's present- what color? be sure that you feed her a high quality puppy food from now until she's weaned her puppies (6-12 weeks). Definitely make sure that the puppies recieve all vaccinations (they will need several rounds), deworming, and are spayed/neutered before rehoming them. it is also important to microchip them- microchipping is extremly important -especially in natural disasters when rabies tags/files can be destroyed- microchipped animals during katrina were able to be reunited in huge numbers with their owners because the chips unlike tags/paper can be scanned anywhere and when registered- can help unite owner and animal. you need to charge a fee for adoption- don't do a "free to a good home" add. people specifically look for those and will often use "free animals" as bait for fighting rings. So you will be protecting the pups by charging a reasonable adoption fee to cover the cost of spay/neuter /vacs/etc.
I'm glad you've already thought about making the appointment to have the momma spayed when the babies are weaned -that is very good! Be sure she stays indoors only from now until the time she's spayed and away from intact males.
Also- it is normal for her to start "nesting" right now- she might act clingy, tear things up, chew a lot, loose her appetite or increase her appetite, drink a lot of water, look for a "nest" - this is why the kiddy pool is important!, she will also likely want to be right by your side all the time. that's normal.
also- to answer your question: your lab should be spayed about a week after she finishes nursing/weaning her puppies. you want to wait a week after the puppies are weaned because she will need time for the swelling in her mammory area/reproductive organs to go down so that the tissue isn't too inflamed when the vet does her spay.