you have got up to 90 days to accept or reject your ITA. So the 6 weeks will fall before the deadline. remember you can prepare all the documents , fill in the application and wait for the last supporting document before you submit and pay for your application on line. If your Pcc is delayed and does not reach you on day 89, then press the decline button. don't forget it!!
Better yet, if you have got a receipt and proof that you applied on time for your PCC, you can upload that with a letter of explanation together with all the other documents. That will be accepting your ITA and it should be fine.
Bottom line, if you are not ready, decline the ITA, you will be put back in the pool and with your nomination, you are guaranteed anothet ITA in the following draw.