If one cuts his fingernails on Thursday night, does he comply with the mitzvah of cutting nails erev Shabbos, or is it better to delay it until the next day?
Both are true, preferably the preparations for shabbos should be done Friday morning. The reason is because then it is more evident that it is being done for shabbos. However if doing things on Friday will cause stress, etc (winter months, a lot to do, work) it should be done on Thursday.
As a side point ,regarding nails, they shouldn’t be cut during the day on Thursday, because we don’t cut nails 48 hours before Shabbos as they start growing back 48 hours later and it isn’t kavod shabbos for them to start growing on shabbos. If it can’t be done on Friday, it may be done on Thursday also, which is better than on Wednesday.
MG”A 251-6, Mateh Efrayim 625-11, Likras Shabbos pg 21.