How long does it take to refuel a big jumbo jet?
It depends on a number of factors like:


the aircraft size and variant
the range required
the aircraft load
equipment available
Ground crew proficiency


...among others things.

This figure from the 737 Airport Planning document gives 9 minutes for the fueling time for a Boeing 737-600:



Image from B737 Airplane characteristics for Airport Planning

The following image shows the time taken for refueling a Boeing 747-8 Jumbo to be 44 minutes:



Image from B747-8 Airplane Characteristics for Airport Planning