Question
Is it permitted to get a haircut on Thursdays?
Answer
I believe that some of the commentaries on the Shulchan Aruch (Orach Chaim 260) say that one should not have a haircut on Thursday; rather, the haircut should only be on Friday so that one will look good for the Sabbath. (This reason probably applies to any day of the week that isn’t Friday – though there are some opinions that it is only a problem on Thursday).
However, the commentary Aruch Hashulchan (ibid) asserts that a person is definitely permitted to have a haircut on Thursday if they know that they won’t have time on Friday.
I hope this answer helps.
Rabbi David Sedley