(a) A day, for purposes of determining employment or unemployment, is the calendar day running from midnight to midnight. If an employee begins a shift of work before midnight of one calendar day and the shift continues through midnight into the next calendar day, the day on which the shift began is the day of employment.

(b) If an employee works on a shift beginning before midnight and continues working beyond the end of the shift but does not complete the succeeding shift and midnight occurs during the first or succeeding shifts, only the day on which the first shift began is a day of employment.

(c) If an employee works for two successive shifts and midnight occurs during the second of these shifts, only the day on which the first shift began is a day of employment.

(d) If an employee works for two or more complete shifts and midnight occurs during the first one of these shifts, both the calendar day ending with that midnight and the succeeding calendar day are days of employment.