Is this realistic to do in a day ?

Yes, if you have tickets already reserved for the Opera house tour at 1:30 and know in advance you can check in someplace and get rid of your bags before.

That would be a casual dinner, in that time frame, not sitting down for three courses.

Thanks Laura - yes casual dinner although need to figure out where as we are vegetarian :)

Yes, you can do it.

This is a very realistic schedule with good cushioning between scheduled stops assuming that you are not planning to enter the Arc d'Triomphe and realize that dinner will be probably at a fast food place if the tour starts at 9:15. Just a couple of minor points to watch out for if by "Climb up/ enjoy the view / back down," you mean the dome at Sacre Couer, this will not take two hours and if you are traveling in September through May, the dome closes at 5 PM. Unless you want to be at the Arc d'Triomphe at 6:30 to see the relighting of the flame of the unknown soldier, you can be there and done by 6:30 which will give you more time for dinner. Are you sure about the departure time of the Ilumination Tour and where does it leave from?

Hi JHK -
Not climbing the dome of the basilica , just the steps in front of Sacre-Coeur to get the city view.

We will be there on Jul 17th .

The big bus night tour on its website says 9.15 from Champs Elleyes. Will send them an email and confirm.
https://d12dkjq56sjcos.cloudfront.net/pub/media/wysiwyg/bbtpdf/Paris%20Night%20Tour%20July%202016.pdf

I'd probably take the metro to Sacre-Coeur since you have plenty of time to go up and down. A taxi could take you to the top, other than that, I don't think you need it and it would likely take more time.

Is the 8 AM arrival time for a transatlantic flight? If so, I think you're being incredibly optimistic to expect to keep going until 11:15 PM. There's no way I'd pre-pay for an evening tour on my day of arrival. Actually, I don't pre-pay for anything on my day of arrival. If you're experienced European travelers and know you'll sleep on the plane, ignore these comments.

@ DTraveller, I asked about the time because there is a tour called the illumination Tour that leaves at 10 from Rue des Pyramides. By the way, there are a number of Italian restaurants near the Arc that should have good vegetarian options. When I get a chance, I'll look at trip notes from a trip I took with my niece, a yogi, to see if we have any specific suggestions.

There's a McDonald's near the Arc de Triomphe on the Champs Elysees not much vegetarian, though. There are undoubtedly other places where you can get something to eat, but they all cater to tourists and are very overpriced. Just so you know. The cafes around Montmartre are probably a better bet. The ones right on the Place du Tertre are also touristy, but better than on the Champs Elysees; there are others on the side streets.

If you eat eggs or cheese or vegetarian salades or vegetarian pizza or vegetarian pasta you can go into any cafe or restaurant on the Champs-Elysees and order.
Menus are always posted outside, so you can make your decision before you go inside.

Learn using the metro from the beginning, after a while you will get some routine and see how quick and easy it is moving between places. There is a direct line between Montmartre / Sacré-Coeur and Arc de Triomphe, guess with the metro about 15min. way cheaper and more easy as with a taxi.

Seen your Transatlantic flight it will be better to think doing the illumination tour another day.

http://parisbytrain.com/paris-metro-maps/