How long does it take a pyroclastic cloud/flow to dissipate?

Say I saw one of those pyroclastic clouds from a volcanic eruption heading down the mountain toward my small city. If I wanted to seek refuge, and found a well insulated large stone building with a basement, could I survive the cloud by hiding in the basement? More importantly, if I could, how long would I have to wait until the temperature is bearable and the air outside is safe enough to breathe (provided there is no magma flows)?