I answered 45 minutes but it really depends on the cube and if it's a type of cube I've done before or not. EX: I recently magnetized my second Warrior W. It took like 20 minutes while not rushing. Then I did a 68mm Big Sail. That took more like 45. Could've been faster but I was moving slow for some reason. Maybe because I was watching TV, LOL. It really doesn't take all that long to do a cube once the pieces are all apart. Do a corner/edge pair, wait a few seconds for the glue to set. Pull 'em apart, do 2 pairs. Or, alternatively, pull 'em apart and do one corner piece after another then do one edge piece after another. You can crank through them in 10-15 seconds apiece pretty easily*.
* - until a magnet jumps over to a spot you don't want, gets glue on itself and begins to stick and then you spend 5 minutes separating the two magnets, LOL.