Realistically speaking assuming the PokeWorld Regions are the same size as they are in the Real World how long do you think it would take on average to cover them on foot? To keep it simple lets follow the routes in the games and use that as our walking path.
This should help with locations and mapping the distance.
Also Info from someone who walked across Japan.
145 Days walking plus 27 days of rest = 172, that's just under six months.
He's having trouble with the map on his site, but here it is on google (Note: The Route-in blue-is broken up into three pages).
(May not be the best example for what I'm asking about, but it was stumbling across this that brought the question to mind)
Several additional thoughts: There isn't anything stopping a Trainer from using alternate travel means like a bike or flying or riding on their Pokemon once they become big enough. Which would cut down on travel time...
Also Training/Catching/Badge Collecting/etc. would need to be factored in, but for right now lets focus on just walking through the Region.