How long will a connection stay in server‘s backlog queue

When testing, before accepting, I let the server sleep 15 seconds, during this time I close the telnet client. After 15s, the server still can accept it (then server read it, return 0, and close the client).

What I want to know is, how to set the life time of a client to be accepted in the backlog queue, or it will never be overdue?