--Main Series--
Red - I restarted this one several times, so maybe somewhere in between 60-80 hours combined from all my restarts before now. My current playthrough has only 19 hours logged in it, though, but this one may have a lot in the end since I plan to use this to finally beat Stadium.
Blue - 1 playthrough worth I know for certain, how long it took...I dunno
Yellow - Same as Blue
Silver - All my playthroughs combined I estimate to be about 100 or more hours. Mainly because I loved that game to death at the time.
Gold - Again, just 1 playthrough worth.
Crystal - 40 or so hours maybe?
Ruby - 169 hours
FireRed - 70 hours
Diamond - 80 hours thus far
SoulSilver - 170 hours exact as of now
I have Emerald, Sapphire, and LeafGreen, but I never even played them at all ever since getting them.
So just the main games combined I estimate to be at least 630 hours. But I'm really going from foggy memory on the old games here as well.
This doesn't include the spinoff games either, which I know I've clocked in a nice chunk of hours in Colosseum before my memory card wiped itself. And my 64 is a pain to dig out and check the times on. I have about 22 in the TGC for game boy, not including my restarts. And 16 hours in Explorers of Time.