I am right now going through the same problem you are facing right now.
I have a short film that is needed by this Monday and the picture edit isn't done yet.
I did a lot of work on it (4 complete days) and I have even worldized the whole voice track which is a newscast playing over a TV and there are more lines the editor wants to place in (which I didn't have before i.e. I have to re-set up my worldizing again).
In retrospect, I think what I should have done is:
A) Pulled the backgrounds, spot effects I know I would need, and designed a rough palette of sounds to use when the picture is done.
B) Not worldized anything until it was locked (unless there is no chance of additional material being added)
C) Not synced any footsteps or anything perfectly yet.
Something that will make the changes easier is I requested from the editor an EDL for both the version I am working on now and the finished edit so I can conform using that which will be much easier (i.e. I will know exactly how many frames things shifted and what's a new shot, etc.) This may or may not help you because they are working on CGI shots..
I would ask the editor what shots are going to stay and for sure going to be in the edit and work on those until they are synced and perfect, and anything that might change wait for until the picture is locked - but start getting something ready for when that time comes.
And do make an effort to find out why you are getting it later. It makes it impossible to do your job and it sounds like the visual dept has already missed a few of their deadlines which pushes you back - and that's not ok in my book. Find out via whoever is appropriate (director, producer, etc.) and make sure it doesn't happen in the future if you're working with them again. It endangers your job and it shouldn't be like that, but things like this do happen unfortunately...