This is super variable based on the actual art specs and how used to working in that style the artist is. Assuming they aren't extremely complicated I would expect anywhere from 1-5 production days.
Im not asking how long it will take me. I waa after ballpark estimates on (a contractor) modeling spaceships with 500-1000 polygons in terms of whether im lookibg at hours days or weeks .. anyway ..I'll have some specifics a little later...