Sorry for my bad English... Intel NUC Braswell NUC5PPYH CPU N3700 with latest Bios 0056 and all prev. After install FreeBSD-11.0-amd64 _and reboot_, Intel NUC5PPYH slow Bios starts from Logo to F2,F7,F10 message up to 1+ minute. I am think, that problem in GPT HDD mode and cooperating NUC Bios & FreeBSD GPT, because Bios MBR install mode to fix this problem on FreeBSD. So in GPT HDD mode NUC can slow Bios starts until # poweroff and poweroff my APC electric filter and poweron APC & NUC again. (I am think, as FreeBSD-memstick.img have GPT structure, then no need to install FreeBSD for reproduce this problem enough just load from this GPT USB memstisk and reboot).
My (Antarex nickname) message on FreeBSD forums: https://forums.freebsd.org/threads/49058/ and in this Forum another user (digital_turtle) has reported about NUC5CPYH (analog of 2-Cores of my NUC5PPYH) issue: "I noticed that the Intel NUC POST boot up runs slower after installing FreeBSD (about 1:15 min only to wait until Intel NUC display disappeared [...] but no problem for me since I only used it as headless machine.."
In regard to your inquiry, as you mentioned before, Intel does not test and validate Intel® NUC on FreeBSD OS or TrueOS, as you can confirm on the following link:
What we recommend is basically what you did, which is the BIOS update to the latest version.
So, in this case, in order to get further assistance to try to fix this issue, the best thing to do will be to access the forums or support department for that __specific__ operating system:
For testing purposes, if you have the option to use Windows, that will be really helpful, because if the NUC does the same, then it could be related to a hardware problem.
I have not Windows, so I am try DragonFly BSD (no problem with slow Bios Start on my NUC) and LinuxLite (also no problem with NUC Bios slow starts).
Is it possible to determine workaround in GPT FreeBSD mode (for GPT and UEFI) for this Intel NUC?
The problem is solved in TrueOS since 2016-12-15.USB Image and FreeBSD-12.0-CURRENT.
% uname -a
FreeBSD freebsd 12.0-CURRENT FreeBSD 12.0-CURRENT #0 r318137: Wed May 10 15:09:31 UTC 2017 email@example.com:/usr/obj/usr/src/sys/GENERIC amd64