StartOfADay returns a TDateTime value that represents the first expressible moment of 12:00:00:00 A.M. on a specified day.
The AYear parameter specifies the year of the desired day.
The AMonth and ADay parameters specify the desired day as a month of the year and day of the month. AMonth can range from 1 through 12. ADay can range from 1 through 28, 29, 30, or 31, depending on the values of AYear and AMonth.
Declaration: Function StartOfADay(const AYear, AMonth, ADay: Word): TDateTime;