def say_hello_mass(context: CallbackContext):
    """React on command"""
    # context.bot_data.data = collections.deque([[message_to_user1, user1], [message_to_user2, user2]])
    context.bot_data.users = {...}  # some data inside already
    context.bot_data.users.update({user1.id: "Hello", user2.id: "Bye"})
    context.job_queue.run_once(callback=say_hello_mass_job, when=0)


def say_hello_mass_job(update: Update, context: CallbackContext):
    """Here need to be vigilant to no overwrite a dict/queue with a new call,
       so preferable thar the dict/queue item will contain every required data.
       Therefore, it should be created during app startup and in future only append to it
    """
    for text, user in context.bot_data.users.items():  # Not sure if enumerate will work here
        say_hello_personal_job(user, text, context)


def say_hello_personal_job(user, text, context):
    if user.conversation_data is not None and user is not None:
        context.bot.send_message(chat_id=user.id, message=context.job.context)
        context.bot_data.data[user.id] = None  # Delete are preferable but may break the order
        time.sleep(1)  # UPD


def end_conversation(context):
    context.job_queue.run_once(callback=say_hello_personal_job, when=0)  # In
    return CH.END