Good morning Rox, welcome to BYC.
I have 3 dogs that I have introduced chicks to twice so far. For me we start as soon as the chicks come home. We safely let the dogs sniff, see, and hear. Each dog is an individual. 1 has strong prey drive, 1 is a heeler, the other a food bully. My dogs know I am the alpha and I make it clear that the chicks are not food, prey, or toys. The chicks look and sound so much like the fluffy, squeaky toys my dogs love to rip the stuffing guts out of! Every interaction is supervised until I am confident with the dogs behavior. My dogs are used to going after anything that doesn't belong in the back yard. Once they didn't know I was out there and they came after me. Of course I was proud, since that's why I have dogs, as a criminal deterrent. Now the chickens are in a tractor until the dogs get used to seeing them and know they belong there. The strong prey drive one pounced at the chick fence when I started the mower the other day, she's not ready yet. The food bully went by them to stand over the food they were eating and stared them down. Now the heeler lays by the tractor all day. He would protect our previous flock when his dog friends would come over. The dogs may just want to play, not kill (depending on the dog). But they don't know their own strength sometimes and is dangerous until they know lips/teeth/ paws are off limits.
Ranging at separate times is a good idea, but if they happen to get out at the same time it's good for your dogs to know what your expectations are. Dogs ultimately are people pleasers for the most part and want to do what makes us happy. They look to us for guidance. It can be done, many people have all kinds of animals together, cats dogs, chickens, multiple roos, pigs. However I started with chicks so the chicks weren't already conditioned to react excitedly when the dog approaches (seems easier for me). And I have very good communication with my dogs. If you are close to your dogs you will know when the time is right, if ever.
Chicks grow so fast, I'm glad you are enjoying your new adventure!
Spark, also welcome to BYC!