The same exact thing happened to me. I called a couple months before our trip. I, too, was told I called too early and I should call 2-3 weeks before our trip to schedule a tour. Life happened, and I forgot to schedule the tour before we went on our trip in June...if I don't do something the minute I'm thinking of it, I forget!
On our last day in WDW, we happened to be hoofing it to our lunch ressie at Beaches & Cream. It was CRAZY hot, and we had a few minutes to kill, so we ducked into the
DVC model on the Boardwalk just to get some AC and take a peek. The DVC guy struck up a conversation with us and urged us to do a tour. When we politely declined as we were headed to lunch, he urged us to do a tour after lunch. He even threw in a $50 Disney gift card and FPs to sweeten the deal. We wound up doing the tour after lunch while our teenagers walked to DHS. While we did not purchase DVC on that tour, we were able to use the gift card toward our hotel balance and we were able to use the FPs before we left that day.
So, if you really want to schedule a tour before you go, put a reminder on your calendar. If you forget, no worries! Just go to one of the models any time. DVC will make it work either way! Have a magical trip!