It all depends on what you have installed. I have Windows 10 installed on an old Hitachi external hard drive and it boots faster than Win 7.
Note: I use 360 Total Security to measure my boot time, it measures the time from bios to when 360 TS loads, which is the last thing to load during boot.
Also, I have found that when the black screen shows up, if I hit the Enter key, things get going. Guess I should give feedback on this, as it's been happening for awhile now.
Few things to shave couple of seconds of BIOS time (for legacy BIOS). All the automatic settings on manual with same values as it was on auto. Turn off SMART check and eventually all the devices not used. UEFI is different animal because during the POST it has to load stuff from disk and that goes much faster on SSD or fast HDD.
Performed a clean-up on the registry & defrag on HD (not SSD).
Re-booted the PC with a start up time of 100 Secs (no change from previous so this made no difference).
Shut down Windows rather than perform a re-boot.
Switched PC back on & start-up time significantly reduced to 40 Secs & noticed that screen went black for considerably less time.
So it appears that during a re-boot something causes the start up time to increase due to some activity during the period the screen goes black between end of the Windows logo & Log-In sequence.
Haven't tried pressing ESC or Enter during the black screen period to see if it can be by-passed.
My total boot time for 10166 is about 65 seconds on a HDD.
Wow! 26 seconds! That's from pressing the power button until I see my desktop.
Then it takes Outlook way too long to start up.