I recently asked a friend if I could borrow his nail cutter, but he told me that he would prefer I do it in the morning because it isn't good to cut one's nails at night. When I asked him why, he told me it's some kabbalah stuff but he wasn't sure. Another friend also told me this, but he didn't know the details. I had never heard of something like this and it seemed kind if weird. Is this a thing? What is the reason for this?
Rabbi Dershowitz at Dinonline quotes the following regarding a source for not cutting nails at night:
See Shu”t Yechave Daat from Rav Ovadia Yosef 4:20 who quotes from Rav Chaim Palagi that according to the kabala one should not cut hair or nails by night. Rav Ovadia disputes this, and claims that there is no problem according to halacha or kabbala to do so at night.
The great answer hazoriz linked seems to be saying the issue of cutting nails at night is due to "nighttime being a time of judgement. Therefore, cutting the nails, which are an area of tumah, would be considered tantamount to awakening the powers of tumah."