This particular setup (hack) does not work on all machines, and I'm not sure it works at all in xenial, given it was reported as bug when it was only an old unix hack in the first place. Try editing the timeout values from 0.0 to simply = 0. This sometimes re-allows the hidden default of 10 seconds to reset on some systems. Bluetooth, and usb keyboards can all have problems with this setup, depending on the BIOS post sequence. Finally depending on your BIOS you may have to hit the shift key at a precise time in some cases and you may have to hit escape or F1 during boot to get the chance to do it if you are under quick boot. It's a dated wasted hack in the first place, and not reliable except with a ps2 keyboard, and legacy only board, running posted boot. Better ways to accomplish what you are trying to do. If you make Windows the first entry in grub the computer will boot into Windows first doing nothing, and almost immediately just by hitting >enter as soon as grub appears without having to scroll and select it from the grub menu, so why hide the grub menu and mess with the timeouts? I can't see any sensible purpose for this, as it was only invented in Ubuntu kludge to solve some old BIOS issues with grub that don't exist anymore.
TC
