Kids and Dogs
When we first brought Breccan home from the hospital, our 65 lb clown of a Siberian Husky bounded toward his carseat, sniffed him, and gave him a huge howl of a hello. The first few weeks Breccan was home, Ger lovingly watched over his bassinet, cuddled with him on car trips (supervised of course), and hovered over anyone holding him.
For "Brother Ger", as he became known, the novelty soon wore off.
It isn't that Ger suddenly hated Breccan; he just became relatively indifferent to him. He kept his distance. We realized the hovering had become less about protection and more about jealousy (picture Justin Timberlake if the focus isn't on him). We realized Ger really was "Brother Ger" and was having a typical sibling adjustment to the drastic change that, at 6 years old, he wasn't the baby anymore!
Our "two boys" have had their ups and downs. Highs - like letting Ger help clean Breccan when he learned to eat food, Breccan learning to throw a ball and pet nicely, and Breccan requesting to take Ger for walks - are balanced by lows - like Ger getting a touch of food aggression, Breccan learning to climb on Ger and hit him, and Ger missing a lot of walks because of Breccan's various needs.
I searched high and low for the kind of time line you get with "purple crying" or "sleep consolidation". I found very little. I found a lot of sad stories about families rehoming dogs, often times so the dog would have a better life. I definitely couldn't do that to the dog that I see as my first child. I am too selfish that way.
The answer for us, if you want a time line, is that things were not great until around 18 months. Not bad, no real biting or aggression, but a lot of angst and separation, and a lot of guilty feelings. Luckily Ger is very accommodating and pretty lazy for a husky. Around 18 months, B started to understand petting. He started to be able to give Ger treats. He started to be able to talk with Ger and be somewhat intelligible.
Now that Breccan is 2.5, things are starting to really improve. They can "wrestle" a bit, and they cuddle together (supervised) on the couch. Ger seems genuinely happy when Breccan comes home with us and actually concerned when he doesn't. Breccan is able to consistently walk holding my hand, so we take Ger on short walks together. I feel like this has facilitated their bonding. They often are interested in the same things: plants, puddles, sticks, other dogs.
There are still issues. We have a small space, and Ger gets upset when Breccan plays near his food, water, and toys. And Breccan gets mad at Ger for things like being in the way or his food when he's thrown it on the floor.
In the end, the adjustment timeline is probably similar to proper human siblings, and the emotions likewise similar. Dogs, like children, don't get to live perfect lives with perfect parents. In turn, we are certainly not rewarded with perfectly obedient kids and dogs. But really, who wants that anyways!