EWTN Catholic Q&A
Question from tim on 06-17-2017:

is there such a thing as a holy hour in the day I thought 3 in the afternoon was because this was the hour Jesus died

Answer by David Gregson on 01-11-2018:

A holy hour may be done at any hour of the day or night. It is an hour spent in prayer before the Blessed Sacrament. It doesn't have direct reference to the Lord's death on Good Friday, though that may well provide food for meditation on the love of Jesus.