I'm not as wise as GoldenGustie, but if one of my best friends was getting married, I wouldn't miss it. I say this knowing that I would have the discipline to put in the extra study time during the week that I would be missing out on during the weekend.
I actually don't think the first few weeks were that stressful. I spent a lot of time studying, but I think much of that time was really wasted as I searched for an effective and efficient method of studying. Biochem will be your only class during that time, so you won't have other classes distracting you from your Biochem studies.
My advice would be to really focus during your first week, devoting as much time to studying as possible. Then, go enjoy the wedding.