During the old days, there was no electricity. Therefore, the nighttime was much darker than now.Cutting nails in the darkness lets the nail pieces fall everywhere, making it hard to collect and dispose of them.
Those days, there were no nail clippers. Instead, people used only knives to trim their nails. When people utilised knives for nail trimming during the night, there was a risk of bleeding and injuries.
There seems to be a religious motive behind this too. Evening times observe the entry of goddess Lakshmi into the home.
Black magic often demands a broken nail piece or a fragment of a shirt worn by the concerned individual.