When my RB Corey died we got Lacey 3-4 months later, but then we didn't have a dog, just the cats, and we missed having a dog. Having recently lost Mandy, time will tell when we get another dog, but I know we will.
I would never judge anyone for getting another dog even the next day, if that is what's right for them. Some people wait years, I could never wait that long, I love having dogs. I don't feel that 'when' you get another dog has anything to do with how much you loved your RB dog. Everyone is different.