I just finished Journeys in the Dark solo tonight. My guess is it took me about 55-60 hours to play through the core quests.
How long do you think Road to Legend is?
How about the other expansions?
Length of RtL vs JiTD vs expansions?
I'd estimate a RtL campaign at 40 to 80 hours.
Well of Darkness has 9 quests, like the base game. Altar of Despair has 6. I think Tomb of Ice also only has 6, though I might be mistaken. Number of quests certainly isn't the only factor in play time, but it's an important one.
What do you consider to be "playing through" the quests, though? Play each one once? Play each one until the heroes win? Play until you get bored with them? The difficulty level of some WoD quests is considered to be fairly ridiculous.