Starting on time is an important rule to live by in the life of the church.
Starting worship on time signals to guests (and regular attendees) that their time is valuable and the church respects their time enough to start when you say you are going to start.
Starting worship on time signals to guests and regular attendees that you take the presentation of the Gospel seriously enough that it is important to your church to start on time. After all, God is a god of order, not chaos. Starting on time signals an attention to detail and a level of organization.
Not starting on time on a regular basis signals the exact opposite (your time is not valuable and we do not care enough about presenting the Gospel with excellence).
Hey! Everybody runs late from time to time. When it becomes a way of life for the church the church might want to ask what message it is sending.