It all depends on the school, but in general, mid-summer is when many begin releasing their new packages. There is no guarantee questions will be the same, although there have been many cases when they have remained so. You would not be hurting yourself by going ahead and thinking through last year's questions, because even if they change, the questions will likely cover the same general areas. All b-schools have a similar thread in their questions and are essentially looking for leadership, maturity, vision, accomplishment, and ways in which you stand out from the crowd. Go ahead and begin assembling stories from your experience which speak to these things and you will be well on your way. Just make sure you download the actual questions when they are released--you don't want to accidentally submit last years! Good luck and I applaud your starting early.