For the second part of the question, re:1725 departure: YES. You must wait until 48 hours before the actual flight. CX does not do 48 hours prior to the itinerary, as some airlines do.

For the first part, a follow up question for you: Is there no icon to check-in, or does it say "Proceed to airport for check-in?" Not sure if it's the first, however if it's the second the reasons I've encountered before are a.) I made changes to the ticket, and then paid for changes on a different credit card b.) The travel agent has not actually issued the ticket yet, c.) I had multiple flights booked on the same day (say one to TPE, one to SFO, one to PEK) and forgot to cancel the ones I wasn't going to fly.