No one replied to this. I wanted to reply to myself help others in this situation in the future.

I was not able to select my seats in advance until online check-in, which oddly was not at 24 hours in advance but rather about 47 hours pre-departure. I got the notification via email from Saudia. Choosing seats was really easy to do, though. However, I suspect that some people were able to select in much further in advance since there were only 6/24 business seats available to choose from for my latter leg.