What is the origin of the phrase "the eleventh hour"
Solution 1:
Its origin is biblical and refers to the parable of the labourers in the vineyard (Matthew XX)
The OED gives some indication of the etymology of the modern expression from as early as 971AD.
eleventh hour: the latest possible time, in allusion to the parable of the labourers ( Matt. xx.); also eleventh-hour used attrib. or as adj.
971 Blickl. Hom. 93 Eall eorþe bið mid þeostrum oforþeaht æt þa endlyftan tid þæs dæges.