On Windows 10 with a SSD, how can I decrease boot times?

Did you install it in UEFI mode?

https://www.youtube.com/watch?v=amwujljr7pY

First of all, no one cold boots ANY version of windows to desktop (fully loaded) in 6 seconds. Those types of load times only happen if your system was in hibernate/power down mode. M$ built a couple of cheats into windows 8 (and they were inherited by 10) to make it look like it booted "really fast". One of those cheats was to never "power down" but rather go into a "pretend" power down mode, which was just hibernate mode. My laptop does this because i want it to do this, it takes about 6seconds to "boot". My desktop however has hibernate mode disabled, and it NEVER hits 6 seconds on boot, because when i want to power my desktop down i don't mean for it to go into some sort of hibernation mode, i want it to turn the f- off. The other trick M$ pulled to make windows seem like it was booting fast was to change the order things load, in windows 7 the last thing that loaded was the desktop, now it's one of the first things that load. So while you might hit the desktop fast in win8/10 there still is a lot of things loading in the background.

Now as to your questions -
the sata ports matter, but you have it on on the right one
Samsung RAPID doesn't help with booting, rapid really creates a quasi ramdisk, and it happens after the system boots, so you'll get no help there
There should be a fast boot option in the bios, which can help you jump past a bunch of stuff when booting, that should speed you up a bit
-on the issue of the bios there are a bunch of boot options you could turn off to speed up the boot at the bios level
-things like LAN boot, SMART checks, RAID checks, RAM checks, it depends a bit on how your system is set up what you can turn off and what you can skip.
-your system should be in UEFI mode, im pretty sure win10 can't even boot in legacy, so there is nothing you can do there to make it faster
-check the SATA hard drive setup, make sure the drives are in ACHI/RAID mode, not IDE. That should speed you up a bit; though if you have to CHANGE that setting, you'll probably break the windows install. make sure you have your ACHI/RAID drivers and windows repair disk on hand to fix this if you're going to change this setting.
-but i do know fast boot is a an option in those ASUS motherboards

p1-p6 are the intel sata ports the e1-e2 are the third party asmedia sata ports for data drives only.
in the bios under boot make sure quick or fast boot is on. turn off the asus splash screen. turn off legicy boot/cmos in the bios under boot set the bios to boot from efi bios only. use msconfig under run go to boot put a check box on no gui boot so the windows logo wont pop up and waste your time.

15-25 seconds is about what you should expect from cold boot to desktop (ignoring times for login)

depends on the hardware installed, but it should hover right in that zone. -hang on i'll time my system from a cold boot.-