START_OF_DAY

Returns the timestamp of the start of the day (00:00) of the provided date

START_OF_DAY (date)

Attribute of the Date type or date constant or calculation producing a date

Timestamp: the provided date at 00:00

Event.StartTime = START_OF_DAY (Event.Date)

END_OF_DAY, DATE_PART, TIMESTAMP, START_OF_WEEK