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It's a two year long program. Below are my main concerns.
1) Is there a certain specified time frame to enter Canada after the visa has been stamped on the passport? Can I travel anytime before the expiry period?

2) I am planning to reapply to the same course and university again for next fall intake starting Oct 2022. What are the chances that the university will accept me again? Do they prefer new students rather than old students?

How about using the new LoA from same university and course for next fall intake and then travel in next August with the same visa? I know new application does not need to be filed in case of same DLI.
Also you can enter anytime after your visa is stamped. In my case (year 2010, 12 years ago), I got my visa stamped about 4 months before start of my classes. I was allowed to enter anytime before.
 
This is a major risk. I might raise a webform to IRCC and update them about new LoA. However, what happens if the immigration officer at the port of entry denies this request?I have read online that many potential students are sent back from the port of entry and I am afraid I will be sent back as well in such case.
Do not inform IRCC and complicate your case unless you are required by instructions. Do t highlight your case unnecessarily.
 
Do not inform IRCC and complicate your case unless you are required by instructions. Do t highlight your case unnecessarily.

If the original start date was Sep 22 and the new one is Sep 23, then he has to inform IRCC according to their guidelines. However, I also think he shouldn't have any issue when entering using the visa issued based on his Sep 22 LOA.