The muscles around your hip and thigh get weaker after surgery. The weeks after a hip replacement are the time when they most easily get their strength back. Daily exercise is how you use that time.
Little and often works better than heroic efforts. Two short, honest sessions a day - the way the program schedules them - achieve more than one exhausting session followed by two days of recovery.
Report your pain truthfully after every set. The program uses your reports to progress you, hold, or step back. It is built to adapt to a bad day - skipping the session entirely teaches it nothing.