That's because none was in konoha looking at you, petchior. In my server happened a lot of times that i was in konoha doing my things at 14:10-14:20 server time and after seeing a gold icon over a running guy i went back to guild base and plundered him. The point is that if somebody sees you moving, doesn't matter if the time expired, can go to the base and click over your name, but yes, if none sees you in konoha you can reach safely the target.

But i have to admit this was before 3.0, maybe since 3.0 it changed, but i doubt.

Then it changed with 3.0 because before you could still plunder them and was also *erproductive most of the times for the convoyer because if you accepted a mission at 13:59 you had only up to 14:29 to reach the goal and if you were plundered lets say at 14:20 and you weren't able to reach the goal in time you also lost the chance to get the halved reward after a defeat.

Edit: i think it becomes grey if you didn't use any plunder attempt but I'm pretty sure it doesn't become grey if you still have 1 or 2 attempts to use.

Tried it today - were two months that didn't happen to me to not being able to get 3 ss convoys within the 3 hours - and I can confirm my previous assumption. In 3.0 still works like 2.0, my bar hasn't became grey still at 14:26 server time and I'm with 1 plunder attempt left to use.