When to start doing classes

Jess • Married to the love of my life, totally smitten with our little girl and boy.
My hospital offers a few classes and a hospital tour. I'm 21 weeks now and I'm wondering when I should start doing classes. I'd like to do a lactation class, a birthing class, and an infant CPR class but I don't know if this is too early. I also know that with Thanksgiving and Christmas coming up later in my pregnancy, it would be nice to get classes out of the way before the chaos of holidays starts :)
Any tips would be appreciated!