Anyone knows what is witching hour and how to overcome it?

My little cousin had the worst case of witching hour crankies (haha not a real word I know) and it was always at a certain time in the evening, around 6-7pm. My late grandmother had her own theories about this (superstitious ones naturally) but I think she was just tired and overstimulated by then. Plus that time of the day was when my aunt and uncle would come pick her and her brother up. Reckon she knew that meant a long journey to her real home and tiring her out some more? She would calm down after a while, usually after being fed and coaxed by everyone in the house. Reckon the key is patience here, just got to see it through.