* The impossible or absurd: Since yesterday comes before tomorrow, it's impossible for yesterday to be "than" tomorrow. This makes the phrase inherently nonsensical, highlighting the absurdity of a situation.
* A distant future: While not a precise definition, the phrase can be used to suggest a future event that is very far off, perhaps beyond the scope of immediate concern.
* A past that is now gone: It can also be used to emphasize the transience of time, with "yesterday" representing a past that is now over and done with.
Essentially, "hier que demain" is a poetic expression meant to evoke feelings of the past, the future, or the sheer absurdity of time. It is not a phrase to be taken literally but rather enjoyed for its metaphorical and evocative qualities.