From the manual:
chargetime {int}
~Determines how long player must hold attack button before releasing it to unleash CHARGEATTACK.
~{int} is time in seconds.
~ONLY works in CHARGEATTACK animation.
Regardless of what you put chargetime as, chargeattack always requires 3 seconds to perform. Tested with both chargetime 1 and chargetime 5.