#3 - Sept. 24, 2010, 5:12 a.m.
Number of instances entered, Nightarrow, is calculated across all of your characters. So if you have, say, five level 80's who all do Coren Direbrew in under an hour, you might not be able to enter a raid instance afterward as you (the player) have been in too many instances recently.
At this time, there is no known issue with this function. However, if you feel that the system needs to be changed or altered, feel free to visit our Suggestion forums and provide constructive feedback regarding the issue.