David - to give you a slightly more detailed answer - I do not know whether this was a 747-400 or -800 but let's assume it was the former. EDIT - it was the 747-400
The aircraft empty weight is around 187 tonnes.
Maximum landing weight is c297 tonnes (MTOW is over 400t) so there are 110 tonnes available for fuel and payload.
Typical payload for a reasonably full flight with some cargo will be in the region of 40 tonnes so that leaves 70 tonnes for fuel.
Including reserves and diversion fuel this would provide around 7 hours of flight time so on a day where no significant delays are forecast (e.g due to weather) this would mean that a diversion could be carried out somewhere between 5 and 6 hours from the destination without the need to burn off or dump fuel.
EDIT: having seen the flight plot this looks consistent with the circuits the aircraft flew which appear to take around 30 minutes.
Last edited by Doors to Automatic; 8th Apr 2017 at 21:26.