From past experiences, I have learnt that on Colossus, if the queue is full up to where the queueline goes under the main walkway, then if on two train operation, will take around 20 minutes. If on one train, will take around an hour. When walking in the direction of Samurai/Saw, if you look to your left, and the Colossus queue section there is completely full up, two train operation takes around 45 mins, and one train operation takes around 2 hours. As Ashley W said, Colossus is prone to down-time, which will often cause major delays to the queueing time. However, some days, Colossus can surprisingly be quite reliable, and not suffer any down-time. It just depends on the day .