A cricket stadium has 60,000 seats. Fans entering the stadium must go through two steps before they can get inside: First, they have to go through security clearance, and second enter through the gate. There are four stations (one in each corner) for security clearance, and each station has capacity to screen people at the rate of 250/minute. The ground has 5 entrance gates, each with a capacity of admitting 100 people /minute. How long before the match should the stadium start admitting people to enter, for the stadium to be full before the game begins?