1 - 3 horas
One of our users spilled their coffee into their MacBook Air's keyboard. The laptop still worked, but most of the keys didn't.
I dismantled the Air (with my nifty iFixit pentalobe screwdriver), blotted up some coffee dribbles, and let the whole thing dry over the weekend in front of the blast of warm air from a server rack.
By Monday, only the m, period, comma and right-shift keys were still dead. So close, yet so far. So we ordered the part, and it arrived the next day.
I've worked on MacBook Pros, MacBooks, PowerBooks, and iBooks, and this was pretty simple by comparison. Not too many screws, and nothing to fiddly to disassemble or reassemble.
This fix was more time-consuming than anything. Just follow the guide, keep the screws organized as you remove them, and you'll be OK.