Can you convoy after the 9pm (server time) window. Meaning you accept the SS mission at maybe 8.59, but set off at like 9.20 or something. Is that possible?

Perfect! Thanks to reading the reply, I just managed to plunder at 9.10pm (server time), when the convoy window ends at 9pm.

And it seems that the convoy support didn't activate. I spoke to that person right after (well, he spoke to me cause he was pissed), and he had a group mate support, but it didn't appear. So I'm wondering, that is either a bug, or support doesn't work past the actual event time window.