What does matter is once the 2 day or 48 hour period is up, the sufferer must not take any more pain relievers until the 6th day. The sufferer still must adhere to the Rebound Rule and wait the 5 days. The critical step is in not taking a pain reliever for more than 2 days in a row with a total of 5 days in-between. This Rule is primarily for the pain sufferer who takes pain relievers more than once or twice a week. Remember that caffeine is an active ingredient in most prescription pain medications.
Caffeine speeds the ingredients of the pain reliever into the body faster.
A complication arises when the sufferer uses a lot of caffeine via coffee, sodas or any other source on a daily basis. The sufferer comes to need the caffeine and uses it just like another pain reliever. The quick fix of caffeine to stop a migraine should only be employed once or twice a month and only by the occasional migraine sufferer. Otherwise, rebound headaches could occur. I personally experienced the trouble with rebounds for years and didn't know that the medication I was taking to relieve my pain was actually contributing to my pain.