1) Chances are they have another account/a friend/etc that is standing around in Konoha. The purpose of this person is that the SS character will appear even before the Plunder list shows that SS. So when they see the character appear in Konoha, they start clicking the refresh and when the SS appears, they just click to get it. They don't require that split second to see the name of the convoy (in case its from a group with strong support).

2) Convoys can be attacked even past event timing. As long as a convoy runs, it can be plundered. In other ways, accepting an SS convoy at 1.59pm and running it at 2.29pm or accepting it at 8.59pm and running it at 9.29pm, these c*l still be plundered as long as there's a plunderer clicking and refreshing, it will show up on the page.

Lastly, some of them may be using softwares/programmes that shall not be named to aid their plunders which gives them an unfair advantage.

Support do still work outside of the plunder hours, at least I know they work if you accept them before the convoy time ends, but I'm not sure if you accept them after the convoy time (i.e. 2pm and 9pm).