I wanted to share my landing experience since these forums really helped with easing my anxiety. I called CBSA to confirm that 8 to midnight is when they process landing at Niagara.
My SO and I arrived at the Rainbow bridge at 8.45pm by car and we went straight to the borders and gave our passports to the officer. when we advised him that we were here for my landing, he made us park on the left at a building nearby. Another officer came out and filled out a white form where it was noted "flagpoling'. Note that both our passports were not stamped by the US. Going back to Can, we paid $4.75 to the officer and advised we were in the US for 5 min, only for landing. we were told to go the next-door building. There were about 3-4 Immigration border officers and about 20 people waiting. we waited for around an hour before my name was called. The only document she requested was the COPR and proof of address (I provided my drivers license). I additionally had brought with me my student permit, proof of implied status, bank statement but they were not requested. The interview was about 5-10 min and she asked me the questions on the COPR. She advised that the PR card would take around 70 days to the address on the drivers license and I needed to stay in Canada 2 years out of 5. She congratulated me and we were off. By the time we left, it was around 10 pm. I was the last one being processed. Someone came after me, around 9.30pm and they categorically said no, they were close and the guy had to come back the next day.
All in all, it was a relatively easy process. Hope this helps and Good Luck!