As stated by others, Plunder doesn't end. You can still access the menu at any time, you just can't plunder if there is no convoys going. So waiting till after convoy ends does nothing for you if someone is still waiting to plunder.

Secondly, by waiting to do the same thing every day, you've let everyone know exactly when you will run. They know you have to run within 30 minutes of closing, so they can just wait. And since they know you do it everyday, you are an easy target. If you cannot get a strong enough support to protect you, you should try to vary when you run so people don't notice the pattern. You c*so run with other people at the same time, assuming it's a time when there isn't too many plunderers waiting. If you run with a group of last minute guys it might help you escape since there are so many other targets.