It would have to be under six months...trying to think. There may have been a small station that switched then abruptly switched again...or maybe something like 1150
How about an unintentionally short format change at 1150 when some cleaners changed the station on the radio from WAAF to Jam'n not realizing they were also changing what 1150
was broadcasting?
1360 briefly simulast WUMB-FM , does that count?
>>North East RadioWatch: October 8, 2002
WLYN (1360 Lynn) has an unusual temporary format: while its sale waits to close, the station is simulcasting the folk music of WUMB-FM (91.9 Boston), in part because the stations share a chief engineer, Grady Moates. WLYN had been operating only sporadically until the simulcast began.
http://www.bostonradio.org/nerw/nerw-021008.html
And under the listing for WWDJ 1150 on bostonradio.org
>>On October 17 (1996), WROR (1150) became the sixth affiliate of the Kidstar children's radio network, based out of Seattle. October 21st, WROR changed callsign to WNFT, under the moniker “Nifty 1150”. When the KidStar network folded in early 1997, WNFT spent some time doing tests of Digital Audio Broadcasting before becoming a simulcast of country sister WKLB-FM
So from 10/17/96, and it says KidStar folded in early '97...so just a few months
http://www.bostonradio.org/stations/25051
Fybush's 97 year in review said Kidstar folded in Feb of that year
>>KidStar folds, leaving WNFT (1150) Boston with nobody to lease it
So, Oct 96 to Feb 97.