We are leaving September 28, and we just got our travel documents last Thursday (September 6)... there was some lag though, since our documents had to go to our travel agent first, and then she sent them to us.
My travel agent also said that it could be as late as two weeks before you leave before you get your travel documents. I'm glad ours arrived much sooner than that, because I was paranoid about them getting lost in the mail.
Typically, the voucher/ressie package arrives about 1 month before check in. That window might be smaller if you book less than 2 months or so before your check in.
If you don't have this package within 3 weeks of going, I'd put a call in to CRO.