You can be "penciled in" at 24 months. Someone else could come along and get penciled in for the same date/time/locations you want, it's no sort of guarantee - you're just on their radar. If you have a theme park or specialty venue, you can sign a contract and pay a deposit to secure the locations at 16 months. All other locations are 12 months. If multiple people want a certain date/time/location, they will hold a lottery at the 16 month mark.
ETA: When I called they tried to tell me that I couldn't even speak with someone til 18 months - which is probably what they told you. You have to be persistent until you get someone who is willing to pass your information along to a sales consultant. I told them I wanted to do a site visit, so after some pushing, I was assigned my consultant. When he called me, he assured me you can speak to someone at 24 months out (it was 26 months at the time - our site visit is at 24 months). Just hold your ground!