The lag is there whether the grub is called from the external usb or
from the internal SATA disk (to boot the external usb OS). I always have
grub installed at all disks, internal or external. Clarify this further
by stating I normally boot the usb OS from internal grub at my desktop
and boot from external grub at other computers; but the 35 secs lag is
also there at my own desktop when booting that external OS from either
internal or external grub.
To explain "before anything kicks in", that means the computer is
inactive for 35 secs after pressing 'enter' at the grub menu before any
computer activity light is lit/flickering. Verified that booting the
same OS installed at internal SATA takes 30 secs compared to 65 secs
booting the OS installed at the usb.
At grub prompt, 'ls' correctly shows all drives, 'ls' from external grub
will still show all drives but or course with the numbering (hd0) as the
usb drive instead.