24 hours is not entirely accurate. It takes a Fentanyl patch (especially the first one) 24 hours to even start to reach it's pain management therapeutic level. Even so, they will also add breakthrough meds to the mix. If you are hitting the limits or exceeding the prescribed dosage for breakthrough meds ("short term") the docors will use a "titration formula" to recalculate your "long term" pain management meds (the Fentanyl). NEVER exceed your prescribed dosage without specific orders from your doctor. Be sure that you read carefully and unstand ALL of the warnings, precautions and insructions for use for Fentanyl. It can be very dangerous if not applied PRECISELY as directed. It is 100X more powerful then heroin. A cut or torn torn patch can release enough medication to cause a fatal overdose.