Just an idea, there may well be a better term for it.

Some support on the web, e.g.:
"Bristol International Airport and OLT Airlines have announced the introduction of the region's first *day return service* linking Bristol with Bremen and Hamburg, commencing 28th November 2005. Perfect for the business traveller, flights will depart from Bristol early morning and return early evening, allowing for day-trips to these key commercial and industrial German cities."
http://www.bristolairport.co.uk/press/press_releases/article...

Or maybe even "same day return service", as in this example from the splendidly named SpiceJet:
"The new flight will depart Delhi at 0615 hours and arrive in Mumbai at 0810 hours. Same day return service will depart Mumbai at 2110 hours and arrive in Delhi 2310 hours."
http://www.spicejet.com/newspage.asp?strNews=SpiceJet2Kolkat...