I've seen it written as 'when you remember the memories with smiles instead of tears' but to be honest I think I will always have a little cry over my lost little ones every now and then for many years into the future.
I have given it a month since losing Luna and whilst I feel ready (still with great sadness, but there are always bunnies in need of a home) my husband still isn't completely ready and I think it will be a few months yet for him.
I would wait slightly longer than a few days, for my own benefit, because I know how my own emotions work and whilst it won't be replacing Luna, I will feel like I'm putting a ‘band-aid over the wound’ to heal it. I know if I do that then, when I lose the next bunny, it will feel like losing Luna all over again because I never truly got over the raw grief of her death and it will be double the hit.
Only time will tell, and only you will know when you are ready *hug*