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So basically, Arthur went a minute and forty-five seconds over his supposedly alloted time. But, this is supposing Cobb was correct.
In a dream, with Yusuf's sedative, the dream is twenty times the length of the layer above. So, if you spend a minute in real life sleeping, you'll be down in the dream for twenty minutes. So, using this, it would take about eleven seconds for the van to fall to the water, if it took the amount of time that Arthur used. This could be possible, if the van slows after it hits the gate, takes a while to go off the ledge, then falls. This is possible, they may have just not shown it to us. Just a theory, comment below what you think, any other theories.
![](https://i.ytimg.com/vi/gSPqMuYj-9g/mqdefault.jpg)