Typically we’re talking quickly in geologic time.
Beyond that, at some point it stops selecting for existing traits in the population, and you’ve got to wait for mutations to go past that point. Like for example, if you were selecting for height, you could get 7.5 foot tall people pretty quickly, but for 9’, you’d have to have the occasional person be even taller than 7.5 feet, and these days, that’s more pituitary gland tumors, not genetic height.
A giant weasel is called a honey badger… or if you want to get closest to a GSD size, a wolverine or giant river otter.
I suspect this would be possible with lots of mammal species, though you might have some failures in introducing other undesired traits into the bloodline. Certain species that have had bottlenecks like cheetah might be dififcult. It’s certainly been done lots with plants and to some extent with fish. I suspect conservatively evolving fish like gar are difficult, they hybridize in the wild but don’t seem to change much.
Yeah, about 3 feet tall but a hefty 672 or so pounds. Most certainly not a lap animal. About the weight of some ponies. Good spot there, Babale.