When you have an appointment to go before time 10-20 minutes so that you do not hurry, because if not, you may be sent to the deterioration itself and others.
When you have an appointment ahead of time to be 10-20 minutes so that you do not rush, because if you missed may adversely affect themselves and others.
When you have an appointment should be ahead of time 10 - 20 minutes so that you won't hurry because if you miss may negatively to yourself and others.