I believe the reference is to what Nikon calls 'Exposure Delay Mode' (d4 in 'Custom Settings') which can but does not need to be used in conjunction with Mirror Lock Up. Exposure Delay Mode, which can be set to either 1, 2, or 3 seconds, releases first the mirror (in the 'up' position) and then the shutter, making the additional use of 'Mup' somewhat redundant. Hope this is helpful.
Best regards,
Larry