How create an Etag with an expire date

I'm thinking about create an etag with an expire date.

Actually I create an etag with a large number of parameters but I would like to make it with an expire date.

I have the solution to keep an information in the server side but I prefer to encode any information into.

I'm searching the better way to do that.

def etag_max_age(hash_code, max_age=30):
  # do something...
  return etag_with_max_age

def etag_max_age_expired(etag):
  # do some verifications
  return True or False

I'm thinking about a solution with cookie

My solution to the problem would be to add a timestamp to the end of the etag in the form of hash-timestamp. You could then parse that out when you needed it.