How to Change PushON - PushOFF Power Button to HoldON - HoldOFF
Two resistors connected serial, one end to vcc, another to a capacitor. A switch from grounds to the middle of the two resistors. Pick a large value for the resistor between the switch and the capacitor.

The voltage across the capacitor will only trigger a low if the switch is held sufficiently long.

The output can go to a flip flop or a MCU input pin.