Permissibility of joining the Jamaah for asr if the time hasn?t yet set in

Respected Mufti,Is it permissible for a muqeem in makkah to join the asr jamaa’ah in the haram whilst the correct asr time for a hanafi has not yet set in? If it is permissible,then why do ulamaa say that its not permissible for a muqeem to read asr but in its correct hanafi time? Please answer in detail