5th gen only took me about 3 days to finish the main story. My first victory over the whole Elite Four + Alder, however, took me about three weeks 'cause I was so focused on transferring pokemon and filling the dex.
"Remember, remember, the fifth of November,
the gunpowder, treason, and plot;
I know of no reason why the gunpowder treason,
should ever be forgot."
I think this one didn't take me any longer than some of the others really. It takes about a week to get through its normal story, that's because I get distracted with other thing of course. Some versions are harder than others, but this one seemed like an ok difficulty. Trainers aren't out of whack or anything and the gyms, especially the early ones are challenging, not super simple.