As I understand it, the strip, once dipped in your hard earned blood, generates an electric current which is measured by your meter, and it's that bit that takes the 3 or 5 seconds. The calibration stick you get with each batch must give the meter that level of information.
FWIW I've used both 5s and 3s in my Xceed with no issues. The nice thing about the 3s strips is that they don't need as much blood as the 5s ones, which meant (for me at least) that the finger pricker could be set to a lower setting.
Regards, Tubs.