To expand on Jungle's earlier post, big jet engines such as the JT-9 specify checking oil within 30 minutes of shutdown. The sump is located fairly high on the engine and the oil will tend to drain down into the case and give an inaccurate reading after it sits a for a while. At this time you would motor the engine for about 2 minutes to get the oil circulating and then you would get an accurate reading. The JT-9 was also famous for eating (leaking) oil so you would always fill it all the way to the top. 1 quart an hour was not an unusual consumption rate on the earlier engines.