I agree with Hazel.
It also depends on your puppy’s personality though. After one month, I started letting Chance poke his head into Merlin’s cage when I fed him and just kept my hand on his collar in case he tried to lunge. Chance is two now and although he would never intentionally hurt his bunny brothers, I still don’t let them have free range of the floor together. I just don’t want to take the chance that he will accidently step on Bromley or otherwise unintentionally hurt him. He is great with the cats and he and Gypsy even play fight – he is so gentle with her! But she can tell him when he is being too rough with a meow, tooth or claw. We don’t know exactly what his breed mix is, but he is a herding dog for sure (he herds EVERYTHING and has the bark and expressions) like your collie puppy. He is high energy and herders don’t fully mature until they are 3 or 4 so at 2 he is still very much a puppy at times. What we do though is let Bromley have free run of the couch and Chance is allowed to sit up there with him. Sometimes Bromley curls up beside him on the cushions, other times Chance crawls on the back of the couch with Brom! Most of the time though, Chance just rests his head on the back of the couch and naps while Brom cuddles his face.
Chance enjoying some bunny kisses. There is another pic of this on my profile.
I had a German Shepherd before Chance named Sarge who at his prime was 110 lbs. To him everything that was smaller than him was his puppy that needed his love, care, and attention. He would even nuzzle my finches and when one escaped that couldn’t fly, he just put his paws around it and laid there with it contained until I could come get it. He kept nuzzling her and licking her lol. I waited until he was three before I let them have free roam of the backyard together. Sarge had a few litters of pups though and as soon as they started walking I started letting the bunnies out to run with them so they would learn that bunnies are just funny their funny looking siblings.