# For fields that represent time of day (such as `start_time`), devs specify
# the value as a string in form "hh::mm UTC". Where hh is hour, and mm is minute.
# Only the UTC timezone is currently supported.
Then I should be good, I use following pattern to assert the format.
const timeOfDaySchema = z
.string()
.refine((time: string): boolean => /^([01]\d|2[0-3]):([0-5]\d) UTC$/.test(time.trim()), {
message: "Value must be a valid time of day string in the form 'hh:mm UTC'."
});