Do you mean doing your workout at the dojang/gym, and then waiting until you get home before you do your isometrics? Yes, that is fine. You do not need to warm up before doing them, but you can if you want to. No, do not do them with your back to the wall. I said that only as a way for learning to rotate your pelvis to prevent hip pain during the side split. Do them away from a wall, with a chair to spot yourself if you wish.