Is it too short because it's just always been too short?
Is it too short because it's lately become shorter?
First case: that's how they made it, almost certainly a function of the microcontroller, have you consulted the manual to see if it's configurable?
Second case: it's possible that the timing is based on the charge time of a capacitor which has lost it's capacitance and is therefore charging (or discharging) too quickly.