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Wiktionary
chronomancy

n. The divination of the best time to do something, or the determination of lucky and unlucky days.

Wikipedia
Chronomancy

Chronomancy is divination of the best time to do something, the determination of lucky and unlucky days, especially popular in ancient China.

The term "chronomancy", stemming from the Greek word chronos (meaning time), and the word manteia (meaning divination) is also used in fiction to refer to a school of magic involving supernatural manipulation of time.