How's award availability on the later flight? I'd personally go for it if there was a reasonable backup plan. The luggage is the only thing that would give me pause, I've experienced BA Priority tagged bags coming out dead last too many times, though not at HKG.

Assuming you don't have access to Hong Kong e-Gates? I used to years ago and need to renew it in my new passport, makes immigration a non-issue going in and out. If you don't have it yet and you end up with 15-20 mins to spare then go get it, I believe they still do it in booths right behind immigration before you go out the sliding doors, you need proof of your frequent flyer status, not all airlines participate but many do.