The term post- preterite, accepted by the Royal Spanish Academy (RAE) as post- preterite, refers to a verb tense. It is about the time also known as the simple conditional.
It is important to remember that conditionals, in the field of grammar, are those times that place the action expressed by the verb at a point that is prior to the moment of expression, although after another instant in the past.
In the specific case of the simple or postpreterite conditional, the action is expressed as if it had not yet finished. It is common for the post-past to be used to refer to a hypothetical event.
The post-past, therefore, is used to name future actions that are considered from the past. It is also used to indicate possibilities or probabilities.
Let's look at an example: "After the president communicated the names of the new members of the cabinet, his private secretary would announce his resignation . " As you can see, "announce" refers to an act that took place in the past, but after another (the communication of the names of the new cabinet members).
"Just after praying an Our Father and a Hail Mary, the boy would begin to prepare his bed" is another example of post-past. The protagonist would "begin" to organize a sleeping environment after having prayed, and not before.
The postpreterite, on the other hand, serves to enunciate speculation or conjecture: "It would be enough to visit him more often so that Pedro would be calm again" , "It would be around eleven at night when the phone rang" , "They told me that the light I'd be back in two hours . "