Apple Numbers '08 - Manual (Page 235)

Chapter 12 Dictionary of Functions 235
 exact-match: Optional Boolean value; determines whether an exact match is
required:
TRUE, 1, or omitted selects the column with the largest top-row value that is less
than the search value if there is no exact match.
FALSE or 0 returns an error if there is no exact match.
HOUR
The HOUR function extracts the hour from a date/time value. The hour is represented,
using a 24-hour clock, by a number from 0 through 23.
HOUR(date-time)
 date-time: Any valid Numbers date.
Examples
Given the following table:
HLOOKUP(20,A1:E4,2) returns "E."
HLOOKUP(39,A1:E4,2) returns "E."
HLOOKUP("M",A2:E4,2) returns "dolor."
HLOOKUP("C",A2:E3,2) returns "lorem."
HLOOKUP("blandit",A3:E4,2) returns "5."
HLOOKUP("C",A2:E4,3, TRUE) returns "1."
HLOOKUP("C",A2:E4,3, FALSE) warns that the value can’t be found (because there is no exact match).
Examples
HOUR(NOW()) returns the current hour of the day.
HOUR("4/6/88 11:59:22 AM") returns 11.