Hey, I'm a second year chemist. I got my interview invite late November - some particularly organised colleges will be earlier, some later! Definitely don't read into it if someone hears much earlier than you do.
As for preparing, the best thing is just exploring around what you're learning; going in to a bit more detail about the stuff you're actually studying. Why chemical reactions happen is a good book for this, as frankly is wikipedia (don't tell admissions tutors though!). I found it quite useful to get some practice in about talking about it as you might just be used to sitting written exams - ask for a practice interview at school (though it might not be much like the real thing - mine wasn't) or even try explaining some of the more difficult concepts (like orbitals, bonding) to parents.
The actual interview will be going through things that are unfamiliar to you; the tutors want to see you use information you know in previously unseen settings.