That's quite an interesting discovery!
I think many people would enjoy multiple 7-13 minute intercourse sessions throughout the night as opposed to one long 40-60 minunte session, where the body starts to become numb to the effects of stimulation and satisfaction.
Foreplay is, of course, a different matter as it builds up to the grand finale; penetration. The act of penetration should be saved for that final stretch of a few minutes when both persons are in there most aroused state. If the foreplay is good enough, the actual sex should be pretty short.
Damn, now I know how the author of 50 Shades of Grey feels. Just typing about this stuff is arousing.