Three friends who live in the same apartment building leave the building at the same time to go rock climbing on a cliff just outside of town.  Susan walks to the cliff and climbs to the top of the cliff.  Fred runs to the cliff twice as fast as Susan walks and climbs the top of the cliff at a rate that is only two-thirds as fast as Susan climbs.  Ralph bikes to the cliff at a speed twice as fast as Fred runs and takes two hours longer to climb to the top of the cliff than Susan does.  If all three friends reach the top of the cliff at the same time, how many minutes after they left home is that?

Let's think step by step and output the final answer within \boxed{}.
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