Counted from sunrise, not midnight — so "the third hour" is about nine in the morning.
The day is divided into twelve hours from sunrise to sunset, which means an hour is not a fixed length: it is a twelfth of however much daylight there is, longer in summer than in winter. Counting starts at dawn, so the third hour is mid-morning, the sixth is noon, the ninth is mid-afternoon and the eleventh is nearly evening. That last one is why the labourers hired at the eleventh hour had barely started before the day ended.
Drawn at an equinox, when the sun rises about six. An hour was a twelfth of the daylight, so summer hours were longer than winter ones and the clock times are only ever approximate. Night was split by whoever stood guard: three watches in the Hebrew reckoning, four in the Roman one the gospels follow.
Not a word scripture uses. The system is never explained in scripture, only used. The correspondence to clock time is a modern reconstruction, and it shifts with the seasons because the hours divide the daylight rather than the day.