CFAbsoluteTime is useful when you need to refer to a specific point in time. A CFAbsoluteTime value represents time as a number of seconds relative to the reference date of 1 January, 2001 00:00:00 GMT. A positive value represents a date after the reference date, a negative value represents a date before it.
Absolute time can be confusing at first because an absolute time value is literally a time interval (the number of seconds since the reference date), but it is interpreted as a specific instant in time. For example, the absolute time -32940326 indicates both a date and time: December 16th, 1999 at 17:54:34. An absolute time value cannot be used to refer to a date or a clock time independently, it always includes both.