* DEFINITION
* This a set of math functions that deal with time. The functions accept
* 4-digit time values and 4-digit time of day values. Time values are
* interpreted as hours-minutes and are valid if all digits are numeric and
* 9 or less, except the second-to-last digit must be 5 or less. Time of day
* values are valid if they conform to normally accepted clock values of
* 1:00 to 12:59 for a 12-hour clock or 00:00 to 23:59 for a 24-hour clock.
