The 'standard' A330/A350 differences course consists of four days ground school (on a laptop), followed by one APT session and four sessions in the FFS. My employer has added two extra sessions (one APT, one FFS) to satisfy company specific requirements. Frankly, I think that's probably the minimum to properly cover all the differences and to adequately prepare pilots before they hop into the aircraft. After the simulator phase we do two familiarisation sectors in the aircraft (one observation sector and one operating with a training captain), followed by four consolidation sectors in an operating seat before we are cleared for A330/A350 single fleet flying. It's not a trivial exercise and there are a LOT of differences. Mind you, the hardest part of flying the A350 is setting the thing up on the ground!