I lost a friend to a hanging suicide about 30 years ago, so I looked into this. I'm not medically trained, so the following is a summary of what I could discover; please check it before relying on it.
Rigor, either of the whole body, or localized as spasm, is where myofiber (muscle) cells fully contract once they exhaust their internal energy reserves. These cells are relatively tolerant of anoxia, so this doesn't usually start until around 2 hours after respiration ceases, but may occur much sooner if the muscles have been exercising or heated.
Many people who attempt suicide by hanging wrongly assume that it is an instantaneous method. However like any method that relies on depriving the brain of oxygen, loss of consciousness may take up to 15 seconds after blood flow to the brain stops, or several minutes if breathing is stopped but blood flow to the brain continues.
Suicide by hanging often fails to break the neck, and fails to constrict the carotid artery, allowing for vigorous activity by the forearm muscles so that they may become both "exercised" and "heated".
The adrenal stress response increases metabolism within the brain, continuing to burn the small-and-now-depleted energy reserves in brain tissue even after consciousness is lost, which reduces the time during which they could potentially be revived.
Unless the victim is (unusually) strong enough to lift their own weight and relax the asphyxia, and has the presence of mind to do so, they are unlikely to remain conscious long enough for muscular activity to make any appreciable difference to the length of time for whole-body rigor mortis to set in.