The yinrih's torpor cycle isn't synced with Yih's day-night cycle, so it's likely there are no timezones on Yih. Calendar days will likely start at solar noon over a particular meridian, likely Newman's Dale. There will likely be time divisions lower than a day that are named rather than numbered, and the names reflect an ancient Claravian cycle of prayers prayed at specific times. These times will still be numbered for purposes of collation in the same way months are numbered in some places but usually referred to by name in speech and writing. Hearthside may have a completely different calendar that isn't divided into days.
Related: The Claravian calendar and liturgical norms may have varied more widely in the past than they do at the time of First Contact. In particular, Hearthside may have had customs peculiar to itself that were later spread to the rest of Focus after the War of Dissolution and the rise of Hearthside as the center of Claravian government. In particular, Many customs practiced on Yih may have been suppressed by Hearthside after the War as they were seen as too favorable to the corporate wing of the Bright Way.