Yeah, it should take an hour, maybe two at the very most. Here's what to do:

• Trade aggressively early on, especially if you can get the oranges or reds. The light blues or purples are good to. Make "bad" trades with the rest of the properties to get those. And if you and one other player can get each get a monopoly, do it even if it means that it's an unfair trade for you.
• Try to sell or make trades with the rest of your non-monopoly properties for cash.
• Within a couple turns there should be a player or two that might land on your monopoly on their next turn. Look for players that are 6 to 8 spots away.
• Spend all your money buying 3 houses on each of your properties, mortgage everything else you have if you need to. If you can't get to 3 on all of them at least try for 2-3-3 or maybe 2-2-3 if you're desperate.
• This is very risky, if you land on anything with a house on it before someone lands on one of those properties you're probably out of the game, but remember in a 4 person game there was a 75% that was happening eventually anyways.
• If one person lands on one of those three house properties they're probably paying around 500, which is 25% of what they started with, and might be 50% or more of what they have on hand. It's also most of what you paid for those houses. They're in bad shape and you're back to not being in much risk. If two people land on your properties you're doing great and two other players are in real trouble. Your chances of winning the game probably just went from 25% to 50% or more in a couple turns.

Either way, the game's probably over in the next 30 minutes, and your chances of winning are way better than 25% :)