You could do 600 hours fucking easily. Trying to catch all the Pokemon? That'd take forever. I got at least a good 200 hours back in 4th-5th grade.
I really wouldn't know; when I had like 50-60 hours logged on, I had like 200 of them, but my file was erased by my brother, and I didn't have the heart to start that massive quest again. Then again, I did transfer a lot of them from my blue version. All I can remember, though, is that the legendary dogs were the biggest pain in the ass to catch, though.
The monster game I did log 100s of hours into, though, was Dragon Warrior Monsters. That game was so badass when I played it.