Yammer - Time to Respond

Hi,

I've exported files from yammer to get a better insight in activites on the network. I would like to calculate time of response for each message and consequently, average time to reply for the whole network.

There are following columns:

id: message id

replied_to_id: id of message on which id responded

thread_id: original thread 

created_at: timestamp, format  dd/mm/yyyy hh:mm:ss (G)



Does anyone have an idea how can I calculate average time to respond based on this columns?

Thanks