This normal SLP behaviour. You will need to upgrade to NBU 7.6 satisfy your requirement.

Scheduling of SLPs is only available as from NBU 7.6.0.1.

See: 

NetBackup 7.6 Feature Briefing - Secondary operation windows in SLPs

http://www.symantec.com/docs/TECH211111

Yes you need to upgrade to 7.6 in order to use this feature of SLP delayed duplication:

As per the above posts you need to upgrade to 7.6

Then you can enable "Postpone creation of this copy until the source copy is about to expire" on the storage operation dialog box.

Enable this option to defer the job until the source for the duplication is about to expire. When this option is enabled, the job begins four hours before the source is to expire. This default can be changed by changing the Deferred duplication offset time in the SLP Parameters host properties.

What is the use of slp in 7.5 when we can't postpone dupication job

The primary use of SLP is to ensure that all copies are done as soon as possible.
This way NBU tries to guarantee your SLAs, RPO and RTO.

In versions prior to 7.6, you can suspend SLP scheduling manually and then enable it again manually.
There are TNs that describe how to do that.

Symantec listened to customer requests and have now built scheduling into 7.6.

Why put off until tomorrow what you can do today :)

Varma,

Your query brings up a concern that the planned NetBackup SLP setup may not be protecting your data properly.

If you use a Storage Lifecycle Policy to back up your data to disk, and then wait two weeks to duplicate it to the next location, what would be the result if you lost the data center that housed your only current backup?  In a disaster, you would only be able to recover your data up through two weeks ago.  In the case of Exchange, you would have just lost the last two weeks of emails for all of those users.  Imagine having to tell your CEO that all of his emails for the last two weeks are gone, and all of your emails regarding any legal proceedings, accounting changes, and customer communications were lost.  I would expect that they will not be happy.

I would suggest that you upgrade to 7.6, but change your SLP plan to back up to disk and retain for 2 weeks  (for instant recovery), then schedule your duplication to be run during a slow backup period of the very next day.  It should be duplicated either to offsite disk, or to tape that will be sent offsite immediately after creation.  This gives you the most protection because, in the event of the loss of your primary data center, you could recover from the most recent backup, so you might only lose 1-2 days of emails.

Our problem here is we can't upgrade nebtackup currently as we have some legacy databases which run only on 6.5 and 7.6 will not support them.

we need any possibilities if dup jobs can run after backup to disk is completed because there is so much io on the disk