I have found that over the years, the weeks the trips are offered generally don't change much, just the physical dates themselves. So if you look at this year's dates or even next year's when they are released, you can use those to help you decide when you want to go. When we booked our Backstage Magic tour for this past February, we had been looking at the dates prior to the release and noticed that when they did release them, it was the same week as the year prior. So for example, if the trip you are looking at is offered, say the third week of June, you'll find that it will be offered the third week of June next year.
