I have no idea how long it takes to be fair, but for something this size 5 hours wouldn't even come close. Of course it depends on quality. (I could build a WeMade quality map in a day no problem, but they are exceptionally poor as far as detail goes, almost none-existent)
Also depends a lot on the environment. a 300x300 cave +2 small rooms took me 2 long evenings. compared the the 2-3 weeks I've worked on these 2 open maps. Indoor maps are far easier due to limited lighting and already textured 'borders'
-Example, just playing around re-doing the plants on 1 screen size last night i spent 2 hours~. Placing, replacing, checking in-game etc, until i got it feeling right. (Solid working without interruptions would obviously be less) Same process applies to everything really.
That is then replicated across the map at a faster pace. (replicating the shade/flowers in the screenshot above will take at a guess 3~ hours alone for the 300x300 town map)
-I spent a good few hours over a Sunday just doing the back limits on 1 map, largely cell by cell, on a 400x400 map takes time.
Of course i never took this as a job, i take my time, and as stated elsewhere I'm probably a little too OCD about placements (constantly re-arranging things by 1 space to look right until I'm happy with it)
Even treating it as a job with focused progression, i would be surprised if anyone was actually willing to pay the real price for time invested. A lot of the pieces, while they are simple, still take a lot of time to implement.