The phrase "time-of-day" is a modern English compound noun phrase constructed from three native Germanic elements. "Time," from Old English 'tīma', originally conveyed a general sense of a period or season. "Day," from Old English 'dæg', referred to the daylight period but expanded to mean a full 24-hour cycle. The preposition "of" functions as a genitive linker, creating a possessive relationship meaning "the time belonging to a [specific] day." The logic of the phrase is transparently literal, directly combining these core concepts to specify a moment within the diurnal cycle. Its evolution reflects the analytic nature of English, forming precise meanings through the syntactic combination of simple, foundational words rather than through morphological fusion.

Structure: time (period) + of (belonging to) + day (24-hour cycle) time: Old English 'tīma', of Germanic origin; related to 'tide'. Functional role: primary noun, the concept being measured. of: Old English, of Germanic origin; a function word indicating possession, origin, or association. day: Old English 'dæg', of Germanic origin; the fundamental unit of time measurement.