I was talking about something abstractly like that map in terms of features (rather than quality). I'm not familiar with the game, but I'm guessing it has several maps, each with different features. There might even be some climate zones.
If you have 100 tiles and spend 5-10 minutes on each, working nonstop, that's 12.5 hours, which you multiply by pi because all time estimates should be multiplied by pi.
Basically, there will be a lot of extra time on top because the something was done wrong (miscommunication) and needs to be redone, and maybe the mountains looked peculiar so you spend an hour or two fiddling with those, and some beach seams needs fixing, then there's the little towns and buildings which can be unexpected extra assets. And woops, client wanted combinatorial roads too. And then the tiles needed to be fiddled together on a sprite sheet a certain way. And then there's the first hour of two before starting, just figuring out how to do stuff efficiently, and understanding the client's needs and... tolerances. Maybe he wants a few initial style tests?
But like I said, if the artist knew exactly what to do and got free reins (client will be left with whatever comes out), maybe a full days work (probably split into 3 because communication lag). It's a lot different to just draw something and to draw something for someone else. I'm also assuming the artist isn't sloppy and puts some love into cliff edges and stuff.
If we're talking Ludumdare speed & quality, maybe 4hrs. Perhaps the same for just replicating the particular map that I linked in about the same quality. But that's probably not what the client asks for unless it's some kind of fan game.
Edit: I see now that OP mentioned SNES "quality" so it seems we're talking lower end here. A smaller studio could keep the costs down by figuring out what is needed, limiting the amount of blind alleys run into... but since the post was so vague...