You have to land at T8 and then walk or catch the AirTrain to T7. You then have to reclear "security".
I'd say 1 hour would be ok if everything is on time and there are no issues at "security" and that you are in good shape with no luggage to reclaim/recheck-in and that you already have your CX boarding pass. This gives you very little margin for error, but that's about as low as I would go. More would be better.
I'd give myself more time just to enjoy the CX/BA/QF lounge at T7. It's not bad.