1) do u hv echannel access
1a) if no, is this the inbound leg of your trip, will you have a transit in hkg for your outbound - if you also have some ffp status, register for echannel access.
1b) re immigrations in general you will be fine. my biggest worry is luggage having constipation along the delivery system. I’ve waited for 45-60 mins a few times in the last 2-3 years, and this is with j/f tags on cx. assume your usm flight isnt delayed, you’d still have some buffer between immigration and checkin deadline (exc picking up luggage).

2) assume you’ll have a 10 minute delay and a 60 minute luggage wait, you still have 10 minutes to clear customs (they dont usually stop pax of yellow of white colour, thats just the way it is). all its involved is to go out to arrivals hall, go up, and get to the checkin area.
if you use self checkin or have status, 10 minutes is plenty (also, the 50 minutes deadline is not the real cutoff for cx. the hard limit is 40 minutes... but i do not know if they use this as a buffer for queuing or whatnot)

that said, i think in most case you will be accomodated if u miss your flight and isnt particularly off an S