Experience and commonality of cockpits / operation of Airbus types means you can convert from A320 to A380 in around 5 hours.
Not to any sort of acceptable standard.
CCQ from 330/340 to 380 requires some 18 hours in the APT(procedures trainer) and another 28 hours of Full Flight Sim.
The ground portion takes about a month and line training can take another month depending on rostering.