The duration time of a program is dependent on the number of the program. The duration is also dependent on how long the Nucleofector® System has been turned on as well as the number of Nucleofections you have done in the last couple of minutes. When the device is initially turned on or if there is a long break between Nucleofections it might take longer than if you do several Nucleofections in row. The program itself has the same duration every time. The increased duration of the pulse is only indicative of the time it takes for the device to charge before delivering a pulse.