when you plug in ( and if you don't have a delayed start time set ) the display in front of the Steering wheel will show a PLUG symbol and after a few min it will display a charge duration, its an approx time and only seems to be in 15min blocks - alternatively the iPhone/Android APP will show the same data...
when the battery is fully charged the flow of current is turned off ( it actually reduces gradually over the last 45min or so... )
you can safely leave it plugged in as if you set a PRE-HEAT/demist/cool function timer it will restart the charger to keep the battery topped up - ALL the vehicles services draw power from the BATTERY, the mains supply is only connected to a charger in the car.