I didn't have an AIX box to try the command on, so I mocked up some (what I thought reasonable) output, and was able to do what you are trying with this:

echo "`date +%s` boxen foo Test message 123456789012345" | perl -pe 's/(\d{8,})/scalar localtime $1/e;'
to get
Fri Aug 15 12:23:47 2014 boxen foo Test message 123456789012345

Hope that helps.