It usually takes 4 - 6 1/2 hours from full discharge to full charge... but when the green light is solid, it's charged enough. After awhile the charger will know when not to charge anymore and it will turn off so there's no danger of overcharging as long as the cradle is plugged in to a power outlet.
Also with the MX700 there's no memory effect, so you can use it with a partial charge without detriment (i.e., no need to fully discharge before charging again).