So, you are running convoy past the actual time of event and wonder why someone can plunder you past the time of event? Hmmmm...

It would be an actual bug if you could accept convoy during time of event then run it after it ends but plunders wouldn't have that option. Pretty cool bug to abuse, don't you think? If that was a option then everyone would start running it this way and no chance for plunderers.

And yes you always can plunder as long as there are some convoys accepted before the end of time for that event.