Potential 72 Hours in Beijing

Hello! I have read this (very helpful!) article and just want to triple check that Hong Kong is an option as I'm weighing all options.

My plan is to travel to travel as follows:

Japan (Tokyo or Osaka) > Beijing 72 hours > Vietnam

It may be that in order to reach my destination in Vietnam I need to travel to Hong Kong first (due to airline points I'd like to redeem). If that's the case, it would be:

Japan (Tokyo or Osaka) > Beijing 72 hours > Hong Kong > Vietnam

Are both of these options possible?

Thank you!