It's unusual to specify a start time for council meetings in the standing orders. The only reference to meeting time in the model standing orders is for the Annual Meeting, and it isn't a fixed time. It merely states that:
"If no other time is fixed, the annual meeting of the Council shall take place at 6pm."
Times of meetings are usually decided when the dates are set at the annual meeting. The fact that you are starting at a different time has no effect on the validity of the meeting.