The present invention is directed to a method and an apparatus for use in a wireless communication system. Specifically, the present invention is directed to a method of performing random access procedure for network access and an apparatus therefore, in which the method comprises: receiving a first downlink signal including first information at time t1, the first information indicating a first time duration T1; receiving a second downlink signal including second information at a time t1+b within T1, the second information indicating a second time duration T2; and performing the random access procedure for network access, wherein if T2 is larger than b, the random access procedure is allowed after T2−b has passed from t1+b, wherein if T2 is equal to or less than b, the random access procedure is allowed after t1+b.