You can in fact state the retention time for the clone from the command line 
(see below). This is what the books says. 

However, as you stated problems, i have verified the issue and in fact there is 
a problem.
First with NW 7.6.1.6

This is what you will see when you run the command:

C:\>nsrmm -o recyclable -S 3591584401
Mark save set 3591584401 as recyclable? y

C:\>
C:\>nsrstage -vvv -m -b "Default Clone" -y 07/05/2020 -S 3591584401
Obtaining media database information on server 2003r2
80470:nsrstage: Following volumes are needed for cloning
80471:nsrstage:         2003r2.001 (Regular)
79631:nsrstage: Migrating the following Regular save sets (ssid/cloneid):
        3591584401
5874:nsrstage: Automatically copying save sets(s) to other volume(s)
79633:nsrstage:
Starting migration operation for Regular save sets...
6217:nsrstage:   ...from storage node: 2003r2
5767:nsrstage: NSR server 2003r2: Cloning requires two available enabled 
devices.
5766:nsrstage: waiting 30 seconds then retrying
5767:nsrstage: NSR server 2003r2: Cloning requires two available enabled 
devices.
5766:nsrstage: waiting 30 seconds then retrying
6220:nsrstage: nsrclone command has retried 2 times.
  .....

In fact the process hangs. The message ...

"nsrmmdbd Media DB error: Save set ssid:3588482332 cloneid:1309224608
eligibility can not be cleared, retention time must be adjusted first "

... is only stated in the daemon.raw file.

I clearly consider this a bug.

-----------------------------------------------------------------------

The behavior does improve with NW 7.6.2:

C:\>mminfo -avot
 volume        type   client           date     time         size ssid      fl  
 lvl name
2008r2.002     file   2008r2          05.07.2011 19:04:26   54 MB 4262675484 cb 
manual D:\

C:\>
C:\>nsrmm -o recyclable -S 4262675484
Mark save set 4262675484 as recyclable? y

C:\>mminfo -avot
 volume        type   client           date     time         size ssid      fl  
 lvl name
2008r2.002     file   2008r2          05.07.2011 19:04:26   54 MB 4262675484 cE 
manual D:\

C:\>nsrstage -m -b Test -y 07/05/2020 -S 4262675484
80470:nsrstage: Following volumes are needed for cloning
80471:nsrstage:         2008r2.002 (Regular)
Successfully deleted original clone 1309885468 of save set 4262675484 from 
media database.
Completed recover space operation for volume 1262516
Refer to the NetWorker log for any failures.

C:\>mminfo -avot
 volume        type   client           date     time         size ssid      fl  
 lvl name
Test.001       file   2008r2          05.07.2011 19:04:26   54 MB 4262675484 cb 
manual D:\

C:\>mminfo -avot -r ssretent
05.07.2020

C:\>


So you better update.

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