If you want to be sure, let it dry for however long you feel safe, but if it was just on the top of the IHS, it's fine.
As others have said, water doesn't do a thing to electronics, unless it's powered on at the time. There's videos on Youtube where people wash motherboards in sinks, and even whole PCs (sans hard drive and PSU) in dishwashers.
Of course, there's some arguable factors involved there as well, such as impurities and mineral deposits from normal water left behind, or oxidization if it's not dried quickly, but in general, it's not the end if water so much as touches it. With motherboards, you need to ensure the battery is removed as well.
I think I even saw someone doing it to an X58 motherboard on Youtube, so it's not just older stuff it's done with. I think this stuff even gets a wash/bake to clean the soldering off when it's made.
I wouldn't recommend doing it for it's own sake, but water and electronics aren't a bad mix unless current is passing through it. I am researching more on this to perhaps clean an old motherboard and video card from a PC that's infested with a huge smoke smell and film. I've put my keyboard in the dishwasher (a cheap Microsoft one), and it worked fine. The key is making sure it's it dry, and that you take precautions.