Using dentro de for in/within/among in Spanish (time/place)

"Dentro de" expressing time

The preposition "dentro de" is used to express the adverb of time "in" , i.e. to say when something is going to happen:

For example:

This use of dentro de indicates the time that is left until that action occurs.

Use of "en"

Bear in mind that, probably due to the influence of English,  the use of the preposition "en" instead of "dentro de" is sometimes used, but it is not recommended. For example:

We do use "en" in time phrases meaning "within":

Here we are saying that it took half an hour to decorate the cake.

"Dentro de" expressing place (abstract idea)

We use dentro de as a preposition of place meaning physically inside [something]; see Using dentro/dentro de in Spanish (inside) for this. But we also use dentro de as a preposition of place with a more abstract meaning, which is usually translated as as "within" or "among":

See also Using dentro/dentro de in Spanish (inside)