Sorry for posting a comment despite not really thinking about the matter very strenuously.

It seems to me that the post is about the formalisms of temporary utility and constant utility.

It would seem to me that the stamps, as used in the text, would actually provide temporary utility whenever they would make the person collecting them happy for a limited period of time, the same with watching movies.

So if you want to do this total utility thing, then perhaps it simply needs to be formulated in the manner of utility over time. And total utility would be expected or average utility over time.