Actually, I ran a quick test on that because I wanted to know what would happen...
*/5 11-12 * * * root /home/tests/test0.sh
echo $DATECODE >> /tmp/cron_junk.txt
output of cron_junk.txt:
As you can see, it actually went until (5 minutes before) 13:00 even though it was expected to end at 12:00. So, what it seems to be is that for every hour that starts with the number specified in the range, the command runs. So, I would expect that "*/5 9-11 * * 5 command" would run every 5 minutes until 12:00, which may not be the desired affect. (Unless I had done something incorrectly.)