Fish/bird/plant modeling

I am wondering how much time is needed (for advanced and for intermediate user) to produce a model of certain species of bird, fish or plant.
The vital part is to distinguish between, let’s say, 10 or 50 species of houseplant or fish (tuna, herring etc.).
I am aware that depends on individual skills, but I would like to know a magnitude - if it’s like an hour, day, weekend or rather about a month.

And another one: do you think that from one base model of fish it is easier to produce 10 different species or each one have to be done separately?

P.S. You guys are incredibly awesome as I see what are you doing in gallery. I don’t know if some of these picture are ‘blended’ or took with the camera.