HOUR
Returns the hour for a given time value. The hour is returned as an integer between 0 and 23.
HOUR(Number)
Number, as a time value, is a decimal, for which the hour is to be returned.
=HOUR(NOW()) returns the current hour
=HOUR(C4) returns 17 if the contents of C4 = 17:20:00.
See also the following functions:
YEAR, NOW, MINUTE, MONTH, DAY, WEEKDAY.