All things being relative there is so many factors involved in the duration of a dive. The average for recreational divers can be anywhere between 25 to 45 minutes. It mostly depend on the overall depth and each individual physiology. Nobody has the same lung volume and breathing rate. In recreational diving it ends when the no stop or no decompression limit is reached. Or it is limited by air supply. For properly trained technical divers duration is well planned ahead and can last up to several hours.