Does Maximum Landing Weight not influence how long it is before the aircraft can land?
747-400 (in common with most a/c) is certified to land up to MTOW
in an emergency.
Engine fire or smoke in cabin are good examples of when to forget the weight and land ASAP (runway length permitting).
Overweight landing inspection is mandatory, but often reveals no problems (casting mind back to a 767-300 which landed at Manchester about 30,000kg over MLW a few years back with smoke in cabin after t/o, and was on its way to sunny Florida again just a few hours later).