AsRock H170M Pro4 very slow post with NVMe

I can't find any setting named Compatibility Support Module!
With the updated BIOS I have a small improvement: it now takes 30 seconds from power on to Windows 10 login screen.
Also two things have changed:
(1) I used to see Windows 10 logo for about 10 seconds, now I don't see it, it just goes from black screen to login
(2) I used to see the ASRock logo with boot options in lower right twice - it would appear after about 10 seconds, remain for a few, then go away and reappear for another few seconds. Now it only appears once.

But still, 30 seconds is far too long for this hardware!

Ah, I didn't notice that I had to scroll down within the boot settings to see CSM. Anyway, it was still enabled. I tried disabling it, but that just resulted in me getting dumped into BIOS setup whenever I rebooted, so I must keep CSM Enabled.

Any other ideas?

What a surprise - it doesn't change! Using just second hand of watch, it's no diff. Basically goes like this now:
10 seconds before ASRock logo with boot options shows up.
Another 10 seconds before a blue Windows 10 logo appears.
5 more seconds until I'm able to login.

I used a custom event view that I found somewhere else. I cannot explain the diff of (BootEndTime-BootStartTime), there's no way that 1 minute 49 seconds have elapsed.
Event Log shows this:
BootTsVersion 2
BootStartTime 2016-12-27T00:23:49.881526900Z
BootEndTime 2016-12-27T00:25:38.346421100Z
SystemBootInstance 3
UserBootInstance 3
BootTime 17221
MainPathBootTime 4521
BootKernelInitTime 35
BootDriverInitTime 108
BootDevicesInitTime 476
BootPrefetchInitTime 0
BootPrefetchBytes 0
BootAutoChkTime 0
BootSmssInitTime 1589
BootCriticalServicesInitTime 236
BootUserProfileProcessingTime 116
BootMachineProfileProcessingTime 23
BootExplorerInitTime 1309
BootNumStartupApps 16
BootPostBootTime 12700
BootIsRebootAfterInstall false
BootRootCauseStepImprovementBits 0
BootRootCauseGradualImprovementBits 0
BootRootCauseStepDegradationBits 0
BootRootCauseGradualDegradationBits 0
BootIsDegradation false
BootIsStepDegradation false
BootIsGradualDegradation false
BootImprovementDelta 0
BootDegradationDelta 0
BootIsRootCauseIdentified false
OSLoaderDuration 1326
BootPNPInitStartTimeMS 35
BootPNPInitDuration 753
OtherKernelInitDuration 135
SystemPNPInitStartTimeMS 885
SystemPNPInitDuration 68
SessionInitStartTimeMS 958
Session0InitDuration 603
Session1InitDuration 157
SessionInitOtherDuration 828
WinLogonStartTimeMS 2548
OtherLogonInitActivityDuration 524
UserLogonWaitDuration 14322

This article from ASRock says:

If you are using a PCIe NVMe SSD (any Intel 750 SSD, and any DC P3500 SSD, Samsung 950 Pro SSD) don't forget to install the NVMe driver that the manufactures provide for their NVMe SSDs.

Click to expand...

Well, I didn't install driver, but my virgin Win 10 install went fine - at least I thought it did. I guess I can now add a Samsung driver? On Samsung web site I find a ver. 1.1 driver with date of 16 Feb 2016 - is this what I should use?

And I see that I may have made a mistake in that a non-boot spinning HD was also present when I did the Win10 install - I don't know why this is supposed to be trouble. And if it is a problem, what to do?

First of all, I want to thank you folks who are helping me with this - your patience is commendable!
I have now reached 21 seconds from power on to Windows login screen - still too long, isn't it? 7 seconds from power on to ASRock logo and boot options.
I now have Samsung_NVMeDriver_2.0.exe (dated 10/14/2016) installed and now NVMe appears in the boot device list. And I have OpROM policies all set to UEFI.

Can someone please tell me what PXE OpROM is?
And when I change Video OpROM from legacy to UEFI, the boot screen (ASRock logo+boot menu) appears to change from 1920x1080 (legacy) to 1024x768 (UEFI). Why?

On the way to getting here, I had some stumbles ...

■ First I changed all OpROM policies from lagacy to UEFI. This was bad, because I lost internet connectivity. The Intel LAN driver claimed to be OK, but Windows could not reach the outside world - couldn't even reach my router.
■ Reverted all to legacy and internet OK again.
■ Installed Samsung driver; reboot. Lost internet again!
■ Changed OpROM policies back and forth - no luck!
■ Removed Samsung driver from Device Manager (but follishly did not remove the software, so it came back and I didn't notice).
■ Still no internet.
■ After LAN driver reinstall (still fails) and some more farting around, at some point I find ethernet driver is all the way back to version 12.13.17.1, dated 6/2/2015 and now internet works again.
■ Now I notice that Samsung driver still appears in Windows Dev Manager and also shows up in BIOS.
■ Updated LAN driver to 12.15.23.8, dated 10/5/2016.

Everything still works, but I just don't know why it should take 21 seconds. And here is the Event Viewer record - wish I knew what most of these things mean.

BootTsVersion 2
BootStartTime 2016-12-30T02:17:14.887089900Z
BootEndTime 2016-12-30T02:19:15.795354000Z
SystemBootInstance 7
UserBootInstance 7
BootTime 15940
MainPathBootTime 4540
BootKernelInitTime 53
BootDriverInitTime 112
BootDevicesInitTime 807
BootPrefetchInitTime 0
BootPrefetchBytes 0
BootAutoChkTime 0
BootSmssInitTime 1407
BootCriticalServicesInitTime 195
BootUserProfileProcessingTime 124
BootMachineProfileProcessingTime 25
BootExplorerInitTime 1224
BootNumStartupApps 16
BootPostBootTime 11400
BootIsRebootAfterInstall false
BootRootCauseStepImprovementBits 0
BootRootCauseGradualImprovementBits 0
BootRootCauseStepDegradationBits 0
BootRootCauseGradualDegradationBits 0
BootIsDegradation false
BootIsStepDegradation false
BootIsGradualDegradation false
BootImprovementDelta 0
BootDegradationDelta 0
BootIsRootCauseIdentified false
OSLoaderDuration 1317
BootPNPInitStartTimeMS 53
BootPNPInitDuration 1066
OtherKernelInitDuration 150
SystemPNPInitStartTimeMS 1211
SystemPNPInitDuration 67
SessionInitStartTimeMS 1284
Session0InitDuration 488
Session1InitDuration 140
SessionInitOtherDuration 779
WinLogonStartTimeMS 2692
OtherLogonInitActivityDuration 473
UserLogonWaitDuration 26636