I have a script that sends me notifications from weechat using notify-send in Fedora 17 64-bit with cinnamon (it's not linux mint, just borrowed some of their themes). The script runs notify-send with an expiration time of 5 seconds / 5000 milliseconds.
[bull:~]$ notify-send --help
notify-send [OPTION...] <SUMMARY> [BODY] - create a notification
-?, --help Show help options
-u, --urgency=LEVEL Specifies the urgency level (low, normal, critical).
-t, --expire-time=TIME Specifies the timeout in milliseconds at which to expire the notification.
-a, --app-name=APP_NAME Specifies the app name for the icon
-i, --icon=ICON[,ICON...] Specifies an icon filename or stock icon to display.
-c, --category=TYPE[,TYPE...] Specifies the notification category.
-h, --hint=TYPE:NAME:VALUE Specifies basic extra data to pass. Valid types are int, double, string and byte.
-v, --version Version of the package.
[bull:~]$ cat bin/beepwrapper
DISPLAY=:0 notify-send -t 5000 'WeeChat!' 1> /dev/null 2>&1
aplay ~/.weechat/bell.wav 1> /dev/null 2>&1
However, these notifications are not going away after 5 seconds, and after a few days, I have 800 something notifications. If I try to click on it, the computer gets sluggish for a while trying to open that many. I'd like for these just disappear after 5 seconds or never stored in notifications in the first place.
EDIT: After more googling, I found 'notify-send --hint=int:transient:1 Test' is supposed to cause the message not to appear in the list of notifications. However, as soon as the notification pop up disappears, it does get stored. Maybe this only works in Gnome 3? Not sure