Though clearly they didn't drive straight to Iowa, because if they were headed to the Pacific there's no real reason they would. It's still an interesting trip, though, because we do know some things:
1) I'm reasonably sure last weeks' ep ended at night, but it appears that they did not opt to stay with Mary at Donna's cabin. They just started driving, but didn't drive far enough away from Minnesota that Iowa wasn't "on the way" a full day later.
2) They got a motel somewhere to sleep, but when Sam's in the doorway it looks like artificial light coming in, so there's probably an interior hall. It could be any time of day in that scene. Which is important, because they have to drive long enough for it to be light at the rest stop when Sam calls Castiel (again) but dark for more driving. I think it'd make sense if they left MN at like 5am, randomly slept through some late morning part of the day, drove, and had it get dark at like 6pm, as it do. Maybe they hit Weather and didn't want to sleep in the car when it was -19, -50 with wind chill. Or didn't want to drive in freezing rain. And then they have to sit around in Iowa for another 12 hours before they can arrange to meet with the bereft twin. (I know the weather didn't look chilly but it's about to be 35 degrees today and it was -35 a few days ago, so like. Anything can happen.)
3) I'm also willing to bet that "on the way" does not mean what the Winchesters think it means. "On the way" is like, driving from Minnesota to the Dakotas and then thinking, "well, I mean, Iowa is still in the same timezone. It is closer to us now than we are to the Pacific. It's on the way!"
4) Winchester perceptions of/experiences of time (especially weird, cutting room floor time) is my faaaavorite thing! Especially if that weird time is spent driving or motel-ing.
Other thoughts that I'm really into right now:
1) They can't just drop their box anywhere in the Pacific, because James Cameron is out there in this little discovery pod, discovering things, etc. So due diligence would really be dropping the box in the deepest part they could find (which, honestly, would either mean a LOT of time at sea or flying to like, Guam and... still spending a lot of time at sea)--the Mariana Trench! Which is, incidentally, where Crowley had to get the First Blade from. Hmmmmmm.
2) Angels/demons can clearly take their vessels all over the place without consequence, but like. I think it'd be interesting if Michael could keep Dean as his vessel alive for all eternity at the bottom of the ocean BUT also had to heed some of the laws of physics. Like, what happens to a body (kept alive) with a Pacific Ocean's worth of pressure on it? What happens to a body (that can't die) when it quickly runs out of oxygen and then has no choice but to breathe carbon dioxide (remember, in this circumstance the lungs haven't collapsed due to pressure)? Does the presence of angelic grace force rapid-scale mutation? Does the lung tissue begin to thrive on new gasses? Does Dean's body become a new life form on Earth?
There are bacterias that 'breathe' gases other than oxygen, but the metabolic reactions aren't as swift as with oxygen. But maybe when you're facing down eternity, swift isn't what you're going for. Maybe when you're at the bottom of the ocean--deeper, even, than the glacial behemoths of the prehistoric deep; deeper, even, than glaciers--swift isn't what you're going for.
Maybe you're more angel than you ever were before, in the deep. Becoming something else. Something slow. Something eternal.