Hello,
If ideal Device time-out does not do the trick in some case, you can try 
nsrjb -u before running label cmd to  ( not sure if it matters, if you 
list the tapes to be labeled in the library and hopefully, networker 
should figure it out that the tape is mounted) unmount the tapes first.
I also  the unmount cmd first before ejecting the tapes every morning.
I do not think that should create any problems if there are additional 
tapes mounted and in use, networker should ignore the tape unmount request 
and error out for any drives currently in use, however, i defer the final 
judgement with input from other panel members.
Thanks

To sign off this list, send email to listserv AT listserv.temple DOT edu and 
type "signoff networker" in the body of the email. Please write to 
networker-request AT listserv.temple DOT edu if you have any problems with this 
list. You can access the archives at 
http://listserv.temple.edu/archives/networker.html or
via RSS at http://listserv.temple.edu/cgi-bin/wa?RSS&L=NETWORKER