Wireshark-users: [Wireshark-users] aggregating packages in one messages

Maybe a silly question, but I am looking for a way to aggregate
packages that belong to one message (I am not sure if I am using the
right terminology). I mean, suppose I send a 10k message from A to B,
then the message is broken up into lets say 10 packages of 1k that
appear in my cap file. I would like to deduct the size of the total
message and the timestamp of the first package of the message from the
cap file. How should I do this?

Thank you,