For short periods of time, prescription medications (such as narcotic pain medications or muscle relaxants) may be helpful to alleviate pain or related complications.
It can take anywhere from 4-10 hrs. now if your head gasket is warped you will have to take it to have it milled that takes from 1 day to several days. if not you can just buy a completely new one that fits perfectly for about $150.
It will take about 8 hours for the beer to re-equilibrate after you dump the head pressure in the keg. You probably can get this done in 24 hours if you are really committed. Dump the pressure the first time at midnight and go to bed. This means your first scheduled sensory trial is at 8 a.m.