The chat thing used to work at any time (almost), but maybe I was using worldwide. I don't remember.
I dont' know now: when we did it, we paid for our own courier to deliver (pony express), and the VFS used their courier to return it. I suppose we filled out a form to let the courier deliver it back to us, and definitely did pay for the return.
Note - if you use pony express, I believe you have to arrange for them to deliver the package during the vfs opening hours, i.e. they can't just drop it in the mail slot. I seem to recall pony express wouldn't pick up sunday evening either, so you want pony express to pick up on a day when next day delivery is vfs office hours.