Hola Felix, 

I think the give away here is in the first paragraph of both of the lessons. We have a combination of words [a + [time] + de] i.e. a certain structure that means "within / after," and another structure [Tan solo + [time] + de] that means "just before" something else happens. These combinations or structures have particular meanings and are commonly used. They don't always make literal sense when translated word by word; we just learn them off. If there is a logic to them I would love to know. 

What I know for sure is that they are good "day to day" spoken Spanish, and go down well with native speakers. Saludos. John