Overall, it isn't that big of a deal if it was really only 1 minute. In some cases, it takes 20 seconds to get normal water flow each time you put the boat in the water. In no case would there be enough heat to break down the oil. It's doubtful there was enough heat to do any damage to the exhaust hoses. Remember, those hoses are huge (compare them to the 2.5 inch on your truck). Perhaps your impeller was run dry. If it was properly installed, it had lube on the fins to prevent any damage.

Always have a spare impeller in the boat, they can fail at any time.