Comment 6 for bug 1401318

"GRUB loading" message comes from the bootstrap MBR code (the ~440 bytes in sector 0) of the boot device and is activated whilst shift is detected.

The boot-strap code then loads GRUB's core image which is what we might call the real GRUB code, where the $timeout value has an effect.

The only way to prevent bootstrap code from displaying the message is *not* to be holding down Shift when it loads. Since the time difference between that point and core image code checking the Shift key flag is probably in the order of a few millionths of a second its not a viable workaround :)