Solutions to problems from delays in channel acquisition by UEs in a contention-based shared radio frequency spectrum band are disclosed. For example, if an eNB knows of a recent or ongoing downlink transmission on a frequency to be used for uplink transmission by a UE, then the eNB may instruct the UE to either skip performance of LBT on that frequency or else perform a type of LBT that is shorter in duration than a full CCA. One way for the eNB to instruct the UE in this fashion is to set an indicator in an uplink grant transmitted to the UE on another frequency. Additionally, in order to avoid truncation of an uplink transmission opportunity, an eNB may notify a UE that an uplink grant is valid for more than one starting point.