Is 10ms Flip to Photon-Start latency normal?

I tried to collect some latecny information using
Oculus Debug Tool and found the data was kinda abnormal.  I was running
oculus-client.exe on an i7 + AMD RX480 machine with CV1.  The GPUView
traces I captured showed that there was only around 4ms between a
present call to the HMD and next VSync.  Could anyone please help
explain how the 10ms "Flip to Photon-Start" is calculated...?