If you don't have a ticket to the party, you won't be able to make a reservation later than 6:55. For a 9:00 reservation, you'd need a party ticket to enter the park. Generally, it will tell you this when you make your reservation.
You have to have a ticket for the party. Once the "party" starts, the CM's will go around the park making sure you have a party wristband. If not, you will be told to leave. They are scattered throughout the walkways and in order to pass thru, you must show your wristband. If you do not plan to attend the party, you should change your reservation for a different time or day.
Everyone in your group has to have party tickets if you want to stay for a 9:00 dinner reservation. Unlike past years, this year the cut off time for dining reservations without party tickets is earlier. For CRT your reservation has to be no later than 5:55.
If you go to the CRT dining reservation page and choose a party night, it will show "Dinner 4:00 - 5:55" and then a second "Dinner 6:40 - 11:20, Special Ticketed Event" meaning you must have tickets to the MNSSHP. It will warn you again later in the process if you try to make a dinner reservation during the party.
Once it is 7:00 castmembers will be checking for party wristbands and anyone without one will be directed towards the park exit so you will not be able to stay in the park for a 9:00 dinner reservation.
I personally wouldn't spend time at a table service meal like CRT during a premium event. Why pay all that extra cash for the event if you're going to spend one or two hours tied up inside a restaurant?