The SUBTRACT-DURATION function subtracts a duration from a date,
time, or timestamp item, and returns the modified item.
The function type is date-time.
The length of the return value depends on the length of the date, time,
or timestamp item specified in argument-1.
The returned value will be truncated to the length of argument-1. 
If a duration is subtracted from a date item, the date returned must fall
within a certain range:
- For 4-digit dates, the range must be 0001/01/01 through 9999/12/31
- For 2-digit dates, the range must be 0001/01/01 through 9999/12/31, but
the year is truncated to 2 digits
- For a 3-digit year (a 1-digit century and a 2-digit year), the range must
be 1900/01/01 through 2899/12/31 (the default). This range can be changed
by specifying the DATTIM PROCESS statement option.
If a duration is subtracted from a 2-digit date item, the range is the
same as for a 4-digit year, but the year in the value returned is truncated
to 2 digits.

Format
>>-FUNCTION SUBTRACT-DURATION----------------------------------->
.------------------------.
V |
>--(--argument-1----argument-2--argument-3-+--)----------------><
- argument-1
- Must be a date, time, or timestamp item.
Argument-1 is the value from
which a duration is subtracted. The duration is specified in argument-2 and
argument-3.
- argument-2
- Argument-2 is a keyword that represents a duration. The valid durations
are:
- YEARS
- MONTHS
- DAYS
- HOURS
- MINUTES
- SECONDS
- MICROSECONDS
PICOSECONDS 
The duration keyword or conversion specifier used must be consistent
with argument-1. For example, the duration keywords must obey the following
rules:
- YEARS, MONTHS, and DAYS can only be subtracted from a date or timestamp
item.
- HOURS, MINUTES, SECONDS, and MICROSECONDS can only be subtracted from
a time or timestamp item.
PICOSECONDS can only be subtracted from a timestamp item. 
- argument-3
- Must be an integer arithmetic expression. Argument-3 is the number of
units of the duration, as specified in argument-2, that are to be subtracted
from argument-1.
Argument-2 and argument-3 can be repeated. There should
be no duplicate argument-2 in one intrinsic function.
Argument-3 can
be a negative integer, but the function only takes its absolute value. If
argument-3 is longer than 9 digits, it is truncated.
If a duration is
subtracted from a date, and the result is invalid, the date is adjusted. For
example, if a duration of 1 month is subtracted from the date May 31,
1997, the result would be the invalid date April 31, 1997.
This date would be adjusted to the valid date April 30, 1997.