You will not be seated, and probably charged the no show fee. You can not utilize a reservation time of 7 pm or later unless you have a party ticket. When you check in has no bearing. They are very strict. You can book 6:55 pm or earlier. After you are done then you are escorted out of the park. I would book a dinner outside at one of the resorts, or another park.
This would be showing on the first page of the restaurants reservation page under hours ..
Breakfast
8:00 AM - 10:00 AM
Lunch
10:30 AM - 2:30 PM
Dinner
4:00 PM - 6:30 PM
Dinner
7:00 PM - 9:30 PM
Special Ticketed Event
- Something like this should have shown during the reservation process ""Your reservation occurs during a special event, which requires a separate admission ticket for park entry. Please ensure all members of your dining party hold tickets for this event."
- Your confirmation email should also include a similar notice, "Your reservation occurs during a special event, which requires a separate admission ticket for park entry. Please ensure all members of your dining party hold tickets for this event."
- And the closer it gets to the time if you have not added tickets Disney may call you to tell you that you need tickets. That happened to me prior to me cancelling mine when I was still debating about party.
Note that at 7 pm they will be guiding you to exit. You will not be allowed to enter any land only head to hub, not enter an attraction, enter a store, purchase food or use the bathrooms. That is how strict they are. I would just head out and go enjoy your evening somewhere hassle free.