Is that like Saint so-and-so's day, or "Ordinary Time" versus Lent, that sort of thing?
Right...there are a lot of references to events in the liturgical year, and things happening "a week after St. John's Mass", etc. Probably a calendar of medieval holy days would be helpful. I know a lot of them, but there are saints that were more celebrated then than now, so I've had to look some up too.