Did you activate Fast Boot?
If so - when booting the NUC - push and hold the power button for ~2-3 seconds (or until you hear a beep, although I don't think the NUCs give any sound. Mine doesn't). This should either give you boot options on-screen, or send you straight to BIOS. Might take a few tries to get the timing right.
The Legacy "fix" isn't really a fix - Legacy mode ("old BIOS mode") limits the capabilities like e.g. proper hdmi audio throughput etc. With these units, you can't have both - atleast not under Windows 7/8. I believe it is in the documentation - although it should be more "pronounced". This, and a decent explanation of both UEFI and Legacy support - what it does, and how it will affect operation and OS. With modern, EFI/UEFI supported OS'es - Legacy boot should be disabled unless you need to use old usb stuff during boot, wich doesn't function witouy Legacy USB support. Some UEFI "BIOS"es can be misleading in regards to this, some have both Legacy (BIOS) boot, and Legacy USB support. As far as can go - try to limit settings to Legacy USB support, and only if needed.