Well the point of the CAT is to make you engage your waking mind in the middle of a dream (DILD). So waking up at 5 on alternate days and 6.30 on the other days, CAT assumes that you don't WBTB. It will engage your waking mind at 5.00 while you are sleeping until 6.30. I've been trying to think of a method to best incorporate WBTB into CAT. Why not try attempting a WBTB at around 4.00 and get back to sleep at 4.30 on the days where you wake up at 6.30? On the days where you wake up at 5.00 you can just sleep through the whole night. I think if you were successful with WBTB + MILD there is little reason to switch to CAT (because it is less reliable), unless you think or you want to find out if it will yield better results.