Wormhole Opens, Four New INTERSTELLAR TV Spots Appear

A couple of months ago any infornation about Christopher Nolan's Interstellar was being treated like highly radioactive material - the slightest hint of who Jessica Chastain is even playing was considered a spoiler. But that's a dumb attitude, because the closer we get to the release date of the movie, the more information the studio will shove down our throats. It's like we're approaching the spoiler singularity for Interstellar, and we're already trapped in its event horizon. 

Cue these new TV spots for the movie, which give away a bunch more about the film's plot - and give a weird piece of info I can't quite reconcile. At one point we're told "Every hour on that planet would be seven years back on Earth," which I kind of don't get. Is this a localized bit of relativity? Why would there be time dilation when you're standing on a planet that I assume isn't nearing the speed of light? Is this just a clunky way of explaining that the planet's rotation is extraordinarily slow (maybe a 168 year long day)? Or is this just a scene where someone is explaining concepst of time dilation using a weird example? I'm honestly super curious.

Also: I like the weird robot guy they have. He's cute.