时刻 has two uses: as a noun meaning 'moment/point in time' (关键时刻 critical moment), and as an adverb meaning 'at all times/constantly' (时刻准备着 always be prepared).
usage
时刻 vs 时候: 时刻 refers to a specific, often significant point in time. 时候 is more general and casual, meaning 'time' or 'when.'
