MQTT Message Format

[nosaj66au]

Hi All,
I now have MQTT messages traveling in both directions in and out of Savvy CAN. Can someone help with the payload decoding.
The topic is the message Id no problem. the last 8 bytes are the data from the message. But what are byte o through 6? at first I thought they were time stamp but I don't think so. Can anyone help?
Also is these any other info around the topic. i.e. I have set my topic a /CANBus0 but the MQTT out is /CANBus0/s/{msg_id} any significance around "s" ?

Regards
Jason