If there is hair to remove, you are not wasting your time. Normally at some point you need more space between appointment in order to have enough hair to remove and then one day, there isn't anything to remove. Also at some point you should need fewer hours a week in order to clear your face. A rough number is it take around 200 hours to clear your face but the number can be more or less depending on the amount of hair to be removed.
The one warning is if you feel the hairs being pulled out, the hairs aren't being killed. You may feel an occasional tug when a more difficult hair is encountered but that should be rare.