I'm taking my comment in stride to answer this in a way that might be the most beneficial to you and Spanish-speaking Japanese learners everywhere.
A "circumstance complement" (lit. from Spanish "complemento circunstancial," it is in quotes because the concept does not exist in English), is a concept in the Spanish language that can describe a circumstance under which an action occurs. Because Spanish most naturally expresses these at the end of a sentence, normally a complete statement can be had without one, and if a question can lead to the inclusion of one, normally this can be called a "circumstance complement."
An example of one of these is the following:
Iré al supermercado.
I will go to the supermarket.
A "circumstance complement of time" would then be identified by the leading question "When?" The answer to this leading question then forms the "complement", as such:
Iré al supermercado mañana.
I will go to the supermarket tomorrow.
However, because Japanese doesn't work in this fashion, it is a bit of a red herring to pursue the question "When is a circumstance complement of time defined as the topic that is marked with は" because Japanese as a language has no such concept.
The "simpler-than-expected" solution is in the inverse observation: That time, among other things, can be a topic. Japanese expresses what phrase in a sentence is the topic by using the particle は. When time is not expressed with the particle は, it is not the topic, and has another function in the sentence. Sometimes direct time is expressed without a particle, and a span of time can be expressed with the particle に.
In the case of the example you've posed, here's a loose translation as it relates to Spanish, with breakdowns:
(topic: 春休み明け)は皆ちょっと(direction: 大人に(verb: 見える))
Just after Spring vacation is when everyone looks a little more like an adult.
Justo después de las vacaciones de primavera es cuando todos aparecen un poco más como adultos.
Therefore, I think you'd do best to focus on the Japanese in the terms of the Japanese language, and not in the terms of the Spanish language, because they work very differently.