I removed the requirement that a layover be overnight. There is no evidence for a distinction in meaning between "layover" and "stopover"; certainly not one based on being overnight. No other dictionary supports this requirement. All the dictionaries I checked just defined it as a synonym for "stopover":
- Merriam-Webster: stopover: a stop at an intermediate point in one's journey
- Random-House: noun 1. a brief stop in the course of a journey, as to eat, sleep, or visit friends. 2. such a stop made with the privilege of proceeding later on the ticket originally issued.
- WordNet: a brief stay in the course of a journey
- Cambridge Dictionary: US for stopover (= a short stay between parts of a journey, especially a plane journey)
- Webster's New World: a stopping for a while in some place during a journey
- Longman Dictionary of Contemporary English: American English a short stay between parts of a journey, especially a long plane journey [= stopover British English]
- Oxford American Dictionary: a period of rest or waiting before a further stage in a journey.
Furthermore, this supposed disction is on its face bogus in the face of the prevalence of expressions like "2 hour layover" and "3 hour layover". Nohat 18:59, 8 November 2011 (UTC)