Actually in the FreeBSD computer world there are now two F2's at boot!
The one you are seeing is FreeBSD F2 from
boot0cfg(8).
You need to hit F2 earlier in the process. Some boards still use DEL or F2 so keep that in mind.
The best chance of catching the bios before booting to boot0cfg is from a cold start.
Reboots on some are harder to get to BIOS.
Basically listen for the beep. That is sometimes too late. Look at the screen. Some OEM'er do hide/mask it.
Tap the F2 gently every 1 to 2 seconds. Not rapid.
Regarding why you need to enter the BIOS, is this regarding Optimus?(dual intel/nvidia video)
Because on newer boards the video is never really 'disabled'.
As long as its built into the cores FreeBSD will find it.
Example:APU2 is headless serial only box. I can show you dmesg that would shows it has video output.
So unless no video on cores then you need to address by the OS to truly disable.
BIOS setting are more for Windows Optimus driver. Directs it which display to use for Windows.