want to change university

I came china for study chinese at nankai university in tianjin. I did starter registration process on web site that's name CUCAS. But i changed my mind because Tianjin is expensive city and i came Xian. My 30 days will finish 22 february. I talked to 2 university in Xian.one of them said "come 21 february" other said 25 february.

What will happen if my 30 days finish. Can i extend this time.