It is called a hard-ticket event. That means that if you purchase a ticket for the Party, you will get in to the party only. You cannot get in with a day regular ticket, and you cannot use your Party ticket to get in during the day. A Party ticket gets you into the Party. So if you want to go to the park that day, you can buy a ticket for that day and just stay in the park for the Party. But if you do not go to the park that day, you will be able to enter with your Party ticket at 7:00. This is the official time. The unofficial time is 4:00 p.m., but it might not be right on the dot. In other words, they will let you in at approximately 4:00, but they don t advertise that.
Just to add some additional information, you do need a separate ticket for the day at Magic Kingdom from the even ticket to MNSSHP.However, even though the MNSSHP event doesn t officially start until 7PM, you can get in with that special event ticket at 4:30PM! This almost gives you a full day in the park, if you stay until the end of the MNSSHP event.
if you wanted to go to the park during the day and also attend the MNSSHP then you would need a regular park ticket as well as a separate event ticket but if you don t want to go to the park during the day then yes you can just buy the event ticket and only go during the event.
You need to purchase a separate ticket for this special event. An Authorized Disney Vacation Planner can help you with MNSSHP tickets. The event starts at 7:00, but you can get in a 4:00 with the ticket.