Yes, Beauty will tell you when those teeth grow in and she really can't nurse them any more without quite a bit of pain. At age 3 weeks I usually have the Mom just come in for visits about 4-5 times a day, and , if she will, nurse them for a few minutes . Then, when she is away from them, she gets to rest and heal. If they are eating well, increase to feeding mash 3 times a day, and leave water available at all times, although they will make a glorious mess with it! At age 3-4 weeks start offering dry kibble about 30 min. before you bring the mash.Take it away when you bring the mash. Soon, they will prefer the dry kibble, they will love to gnaw and crunch it.
As soon as they are able to crunch dry puppy kibble, Mom's job is over and all nutrition comes from you. You have to watch for stomach upsets as the diet changes. I feed a (Second Step) bitch replacement milk from the pet store during weeks 4-5, in addition to the kibble and mash, because Mom will probably not want to nurse them much after that. During weeks 5-8 I feed some plain yogurt and cottage cheese instead of the bitch replacement milk. I start the pupppy vitamins at age 6 weeks. Collie pups are weaned by the end of their fifth week, your breed may be different.
Good luck, and don't forget to have fun, soak up lots of "puppyness" to tide you over those puppyless days to come, and take photos to send to the rest of us!
Marcia P. and the Bonnie Collies