This is a linked open data (LOD) about date and time. "C.E. 1680 January 21" is a date of Julian/Gregorian Calendar (reformed in 1752) (Calendar ID: 101.2).
http://datetime.hutime.org/calendar/101.2/date/C.E._1680_January_21
hcal:101.2/date/2334697.5
hcal:101.2/date/C.E._1680_January_21
hcaldate:2334697.5
hcaldate:C.E._1680_January_21