Call 60 people and notify one person every minute. According to the law, 1 person is notified in the first minute, 1 person in the second minute, 2 people in the second minute, 1+2=3 people in the third minute, 4 people in the third minute, 1+2+4=7 people in the fourth minute. 1+2+4+8+16 = 31person has been notified, and 32 people have been notified in the sixth minute, which has exceeded 60 people, so it takes 6 minutes.