I've had several different strains take 48 hours to start surface colonization, which is what I use as an indication of activity. I always pitch ales at 72. I oxygenate using aviator's oxygen, about 3/5 of the batch gets oxygen. I wouldn't start repitching until 56 hours. Aerate well and pitch at reasonable temps. If you have a clean process, the yeast will start when it is ready.