When mission failures trigger based on a timer while I am away, the timer to allow the mission to be attempted again doesn't start until I log back in.
Example:
I start the Blackjack Addict mission at noon.
I play a bunch of hands and decide to go back to real life at 12:30, return to my condo and close the browser. I come back to the game at 2:30. My "Failure" notice would trigger at 2:30, and I can restart the mission at 2:40.
Normally, if I played it out, the mission would fail at 1 pm, and would be available after 10 minutes, at 1:10.
It may be an intentional feature, but it seems accidental.