When can I receive SMS notification when I change my hard seat to a hard sleeper?

10 minutes. SMS notification is very fast, which is related to the backstage of ticket purchase. You can receive SMS notification within 10 minutes after the hard seat is changed to the hard sleeper. Hard seat is the name for the type of train seat, which is divided into soft seat and hard seat. Hard seats are cheaper than soft seats, and each row is divided into three seats and two seats with an aisle in the middle, that is, the "3+2" seat arrangement layout.