Prepositions of time 3

Antes de / después de + infinitive — Antes de + infinitive = before doing: Antes de salir, llámame. Después de + infinitive = after doing: Después de comer, descansamos. These compound prepositions are followed by an infinitive when the subject is the same; by a conjugated verb with que when subjects differ: Antes de que llegues.

Durante vs por for duration — Durante (during/for) emphasises the span of time within which something happened: Viví en París durante dos años. Por also marks duration but is more flexible: Estudié por dos horas. In many contexts they're interchangeable; durante tends to coexist more with ongoing actions.

Dentro de / hace — future vs past — Dentro de = in (future): Llegará dentro de dos horas (He'll arrive in two hours — from now). Hace = ago (past): Llegó hace dos horas (He arrived two hours ago). These two are often confused by learners translating directly from English.