My quickest presentation was 30 minutes, and could have been shorter only that the conversation switched to something completely different for the last 10 minutes. He (sales) was among the best I've yet met at a Starwood resort, and within a few minutes understand that I buy resale, have no intention of buying new, and really only wanted to hear what was new or changing. He didn't lie, confuse, or otherwise attempt to manipulate my opinion.
I make it clear up front that I have never bought direct, have visited their hard to get resorts, have 400,000+ StarPoints (and don't need more from buying another timeshare), and am there to get a real update and my bonus points. Some of the sales staff ignore me, but when they do I get visibly upset (but I'm not) and stop them immediately - getting them off track and insist on ending the meeting. When this has happened, I'm usually out of there within 15 minutes from that point - they bring in their closer (I think that's a required step for them to get credit for the meeting, or some such), and I repeat myself that I'm not going to buy, etc - and then it's over.
Don't psych yourself up so much that you worry about the meeting, which it seems you may be doing at this point. Just go there, as relaxed as you can be, tell them your goals and after 10/15 minutes tell them to wrap it up. They may say that you need to stay for 90 minutes or so in order to qualify, at which point I would insist on ending the meeting. If you have to, just get up and walk out saying loudly "I always buy *my* timeshares on the resale market for 50% of your prices". If you don't have the energy for this, just sit quietly through the meeting and keep saying "No, I don't have plans to travel next year, and no, I'm not spending any money today. Oh, and no, I don't believe you that this is such a great deal". Get the picture?