Peace be upon you. According to Grand Ayatollah Khamenei and Grand Ayatollah Sistani (may Allah protect them): If there is enough time left before sunset to perform five rak'ahs, then it is obligatory to pray both Dhuhr and Asr. However, if there is less time than that, one must perform Asr prayer as an obligation and make up the Dhuhr prayer later. May you be successful in all good deeds.