I've looked around for this on the forums some, but didn't see what I was looking for, so I'm sharing it here.
I'm currently learning Potionmaking III at a 2284% time penalty. (I'm not in a hurry, so I'm not worrying about brain cap upgrades for now.)
On the website, it shows I have 47+ days remaining. On the Glitch HQ iPhone app, I have 17+ days remaining, a full 30-day difference.
imgur.com/sMzlq (screenshots taken at the same instant)
So, one of those is wrong, my guess the iPhone app.