Author Oliver Burkeman discusses this marshmallow test in his book Meditations for Mortals.

Paraphrasing from memory -

Who is to say that stockpiling as many marshmallows as you can is inherently more virtuous or objectively more positive than enjoying one marshmallow in the moment you and the marshmallow are ready for each other.

"Now" is the one moment you are truly alive. Rest is a concept.