How do I ask / inform my supervisor that I need to take a day off? I just recently got a job as a research assistant over the holiday (which will later turn into an unpaid independent study project). Before hiring me for the job, my supervisor asked me if I would be taking a week off for vacation during the holidays. I told him no. However, for Christmas, I recieved (as a gift) tickets for an afternoon weekday show of an expensive stage production. The show is about an hour and a half from where I live so I would need to take most of the day off. I will be informing my supervisor via email about this. How do I inform him/phrase the email?
XX,

I was just given a surprise gift -- tickets to a show in YY City.  It would be thrilling to go -- any chance you could spare me on Thursday?  Because of the distance, it would mean missing the whole day.  However, I'm free all day Saturday.  If you like, I could come in then to make up the time.

(however you like to sign your name)

Please feel free to adjust this as needed.  For example, you can make the tone less breezy and more formal if you want to.