I didn't receive any acknowledgement email either. I used EMS to send documents so I know their receipt date by online tracking. In my case, they received docs on 30 Jan and emailed me, saying that outcome is complete and has been sent to me via post on 21 Jan. It means it took them about 3 weeks to do that.
On CPA website now it says processing time is approx. 4 weeks.
Once they're done, they will send the letter through post. I saw people getting the letter in 7 - 10 days previously, but not sure about time frame now. My case was a little longer than usual, I guess.
P.S. I'm happy to share :-) I am in the same mood too, waiting for an invite this 22 Apr.