Neither of these concepts are official in the Catholic Church...

Apparition of Mary’s messages at Garabandal…

We must make many sacrifices, perform much penance, and visit the Blessed Sacrament frequently. But first, we must lead good lives. If we do not, a CHASTISEMENT will befall us. The cup is already filling up, and if we do not change, a very great chastisement will come upon us.

As my Message of the 18th of October has not been complied with, and as it has not been made known to the world, I am telling you that this is the last one. Previously, the Cup was filling; now, it is brimming over. Many priests are following the road to perdition, and with them they are taking many more souls. Ever less importance is being given to the Holy Eucharist. We should turn the wrath of God away from us by our own efforts. If you ask His forgiveness with a sincere heart. He will pardon you. I, your Mother, through the intercession of St. Michael the Archangel, wish to tell you that you should make amends. You are now being given the last warnings. I love you very much, and I do not want your condemnation. Ask Us sincerely and We shall grant your plea. You must make more sacrifices. Reflect on the Passion of Jesus.

The 3 Days of Darkness and how they speak of a CHASTISEMENT…
Blessed Anna Maria Taigi (1769–1837) is the most known seer of the Three Days of Darkness and describes the event in this way:
"There shall come over the whole earth an intense darkness lasting three days and three nights. Nothing can be seen, and the air will be laden with pestilence which will claim mainly, but not only, the enemies of religion. It will be impossible to use any man-made lighting during this darkness, except blessed candles. He, who out of curiosity, opens his window to look out, or leaves his home, will fall dead on the spot. During these three days, people should remain in their homes, pray the Rosary and beg God for mercy. All the enemies of the Church, whether known or unknown, will perish over the whole earth during that universal darkness, with the exception of a few whom God will soon convert. The air shall be infected by demons who will appear under all sorts of hideous forms."

Marie-Julie Jahenny (1850-1941), known as the "Breton Stigmatist", embellished the story of the Three Days of Darkness. This will Days occur on a Thursday, Friday, and Saturday, when all of Hell will be let loose to strike at those outside their homes and those without a blessed candle lit. The blessed wax candles must be of 100% pure wax without other ingredients. Such impure candles will not light, while even candles will not light in in the homes of the impious or blasphemers. A two-day period of darkness will precede the Three Days of Darkness 37 to 40 days before, and the blessed candles will be the only sources of light at night during the two days, but can be put out during the day. The blessed candles must be lit for all three days and must not be put out, and any furniture on which these are placed will not shake during the incessant earthquakes that will occur in those days. The faithful are instructed to pray around a blessed crucifix and an image of the Virgin Mary, and to avoid looking out the windows lest they be struck dead.
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Both are chastisements, and it is said that the 2 days of darkness preceding the 3 days of darkness are a period when people will see the condition of their souls. The same supposedly holds true with what was said at garabandal. The visionaries of garabandal forecast a period where people will see the conditions of their souls before the chastisement.