Whilst I'm somewhat out of touch a "day off" is defined as a period free of duty notified to the crew member in advance and from X hour the preceeding day until Y hour the day following.
I worked with one particular set of FTL's where it was an average of 2 days off per week but every so many days one needed a 36 hour or 48 hour break, there was nothing in the FTL's to suggest that those breaks, indeed days off, needed to be at home base although in the spirit of things we did repatriate crew members with their days off at base sooner or later.