set_time_limit() is not allowing any new request on server in laravel?

I have method which need to be execute for long time than usual for that i am using set_time_limit(240) but when I use this method I am unable to made any new request on server i think server gets busy due to this method. I am looking for proper solution. I need execute it for long time because i am reading data from excel file and storing it in database around 20000 records in excel file.

  //delivery zone import function
    public function importDeliveryZone(Request $request)
    {
        set_time_limit(240);
    }

via Chebli Mohamed