Use of imperfect with cuando

[sonama]

In the phrase 'Cuando finalmente llegó el diá de la fiesta', should the verb not be llegaba, since when cuando is used the verb should be imperfect. Please clarify.

[aleCcowaN]

cuando tomaba vino, se emborrachaba (whenever he drank wine, he got drunk)

el día que tomó vino, se emborrachó (the day he drank wine, he got drunk)

cuando toma vino, se emborracha (when he drinks wine, he gets drunk)

cuando el viento sopla, mi ventana vibra (when the wind blows, my window rattles)

cuando finalmente llegó el día de la fiesta (when the day finally came; as soon that specific day came)

You use imperfect whenever the moment the action started and/or ended is unknown, not important or it exceeds the time frame of the paragraph. The day came not a day earlier nor a day later but just that precise day and that was it, hence, it's not the case for imperfect.

[mwtzzz]

llegó refers to a single occurrence
putting "aba" at the end of the verb means something that "used to happen" or "repeatedly" would happen.