Sorry Marco, you may not like my answer, cause it is likely to give you
more work than you expected.

>I have to do
>DELTA_TIME = CAST( <VariableDefinedAsANumber> AS TIMESTAMP );
>right?

No, you're dealing with two different things. A timestamp is a specific
point in time, e.g. 19 August 2002 at 14:04:32.332, whereas what you are
left with after having subtracted one timestamp from another is a duration.
Casting this back to a timestamp is probably not what you want, and e.g. 19
August 2002 at 14:04:32.332 - 19 August 2002 at noon would give you 30
December 1899 at 02:04:32.332 (or something similar). Duration really is a
number, and ought never to be treated as anything else.

Set