1. Day of the Tentacle (about 3 months, before internet - darn squeaky bed!)
2. King's Quest 6 (2-3 years. As a kid, I didn't really aim to finish games)
3. Grim Fandango (1-2 weeks)
4. Chrono Trigger (2-3 weeks - you never said adventure)
5. Full Throttle (2 days)
Longest time to completion: Space Quest 4. About 6-7 years because of timer bugs, completely unfair deaths (as a kid, I thought those exploding sewers were booby-trapped), and the fact that I didn't start using the internet for walkthroughs until about 1998 or so.
After the invention of walkthroughs, time to completion really became a blur. I normally try to beat a game without one, but as I get older, I find that if a game is wasting too much of my time with guesswork (a hour's time wasted, tops), I just grab a hint so I can move on.
