ConnectionConfig.ResendTimeout

Description

Defines the maximum wait time in milliseconds before the "not acknowledged" message is re-sent. Default value = 1200.

It does not make a lot of sense to wait for acknowledgement forever. This parameter sets an upper time limit at which point reliable messages are re-sent.

using UnityEngine;
using UnityEngine.Networking;

public class ExampleScript : NetworkBehaviour
{
    void Start()
    {
        ConnectionConfig myConfig = new ConnectionConfig();
        myConfig.AddChannel(QosType.Unreliable);
        myConfig.AddChannel(QosType.UnreliableFragmented);
        myConfig.ResendTimeout = 1000;         //1 sec
    }
}