There are some airports where CX in HKG cannot issue the return BP. I am not sure if PVG is among them.

Early morning flights are usually on time. So arrival in PVG in OK, but I am not sure about such transit to the return flight.

The departure from PVG is already after 12. That can be an issue. Even if you can get PVG-HKG BP in HKG and rush through everything, if the flight is delayed, you may not make it to the HND flight.

If you are not doing a mileage (or club points) run or if that is not substantially cheaper, I will advise against it. Even if you are doing a MR or such fare is less expensive, I will still advise against it.