When referring to being on holiday any of the following seems possible:
Wir sind über die Feiertage im Urlaub.
Wir sind über die Feiertage in Urlaub.
Wir sind über die Feiertage auf Urlaub.
If we trust Google Ngrams using "im" seems to be quite new. All versions were used the same in the eighties whereas in the seventies and earlier people preferred "auf".
Is there any different usage or connotation of one over the other variant? Is there any reason that "im" gained so much popularity over the other variants?