Point to be noted that scar revision surgery doesn't completely removes your scar. It only makes your scar less visible and possible unnoticeable.
Some factors like size of scar,its depth and its thickless and color of your skin play role in outcome of your scar revision surgery making it less visible.It might take around 1-2 hrs or more depending on your scar.
The healing time and improvements depends upon the type and nature of your scar.All you need is patience as during first few weeks or months your scar might look worst but its natural and final outcome of your scar revision surgery may take a year or even more, so all you need is patience.