The Question is:
How do I convert a selected date (not current) from comparison format to delta
The Answer is :
Comparision format is effectively a specific type of an absolute
time, and is not a format that particularly lends itself to a
simple conversion back into an absolute time format nor into a
delta time format.
Effectively, you will have to convert the comparision format back
to absolute format through manual means, and from there you can
convert an absolute time and the current time to binary, and then
subtract the larger from the smaller value to get the delta time.
The OpenVMS Wizard encourages you to learn about the OpenVMS time
formats, as well as the available DCL lexical functions and the
available system services and run-time library calls. A chapter
on time is available in the V7.3 system manager's manual, and
various time-related operations are in the programming concepts
Some related topics include (3982), (4025), (4982), (5313), (6046),
(6069), (6095), this (6790), and (9713), among others.