incron and have it execute your notification when there are changes in the directory. In your script that is run by
touch a file, if it's been at least five minutes since it was last touched send your notification (using
zenity, or similar).
Another option is
notify-send which is usually in a package named something like "libnotify".
This will display a file count near the upper-left corner for three seconds every five minutes (and stop after 30 minutes):
while (( $SECONDS < start + 30 * 60 ))
if (( ! ( ($SECONDS - start) % (5 * 60) ) ))
notify-send --expire-time=3000 --hint=int:x:0 --hint=int:y:0 $(ls | wc -l)&
Of course, you could just do