Great question!
I would schedule the POPA first, because that takes a little more time. My POPA took about 45 minutes, but my Mayo recruiter suggested to give myself at least an hour for that appointment
Then I would schedule your HR appointment either one hour of 75 minutes after your POPA (on the same date). That way you can finish the POPA and walk over to the HR appointment. The HR appointment takes about 15 minutes.

So if your POPA is at 09:00, I would schedule the HR appointment for 10:15.

Hope this helps!