From now you can change the following settings.

'chat' => array(
        'online_timeout' => 300,
        'back_office_sinterval' => 10,
        'chat_message_sinterval' => 3.5,
      'check_for_operator_msg' => 10,
        'new_chat_sound_enabled' => true,
        'new_message_sound_admin_enabled' => true,
        'new_message_sound_user_enabled' => true,
    ),

• online_timeout - value in secons how long user is considered as online.
• back_office_sinterval - value in seconds, every 10 seconds check for new chats.
• chat_message_sinterval - value in seconds, check for new messages every 3.5 half seconds.
• check_for_operator_msg - value in seconds, check for engage messages from operators interval.
• new_chat_sound_enabled - play sound that new pending chat appeared
• new_message_sound_admin_enabled - play new message sound on new message for back office user.
• new_message_sound_user_enabled - play new message sound for site user (customer)

These settings also can be changed from back office in 

System configuration -> Synchronisation and sound settings