Yes. If your longer game (8 hours) is your top priority, rank it number one. You can then rank one (or more) events in the same time slot after it. If you get your first choice, the system will block out that time period for you and will skip lower ranked events that are a time conflict. If you don't get your first choice, it will then try to fill it with your second choice, third, etc.
Be mindful that the system does NOT take into account travel time between events. So say you have an event at the ICC from 1-3. The system won't let you schedule anything taking place from 1-3, but it will schedule another event, for example, from 3-5. If that other event is in, for example, Lucas Oil, you won't make it in time (and that may be true even if both events are in the same place if they are far enough apart). So make sure to leave at least a little time between events.