The Stay and Scream ticket is basically the same ticket as a regular HHN ticket. The difference is that it's at a reduced price to encourage guests to buy a day pass when buying a HHN ticket. In order to take advantage of Stay and Scream, you have to be in the park before regular closing time by having a regular day pass. Then as Universal is herding the day guests out, show your HHN ticket to the park attendant and they will send you to the Stay and Scream holding area, which I believe is Finnegan's. Therefore, if you have both a day ticket and a HHN ticket, do not leave US at closing time, unless you have something to do outside of the park during that time. You can also go to the holding area prior to the herding beginning.