Let's do the math...
You would need to allow a bare minimum of 1 hour, 45 minutes to de-plane, get transportation (Metro or taxi) to your hotel, check in, quickly freshen up, walk back to Dupont Circle Metro station, take Metro to the Arlington Cemetery station and then walk from the station to the Cemetery. That's not accounting for having to wait for bags at the airport (if you are checking them) nor for waiting around for trains at the Metro station, in case you don't get there just as one as arriving. So, assuming you arrive right on time at 2:55pm, in the best case scenario, you'd be at Arlington National Cemetery at 4:40 pm.
In order to only see the Kennedy Gravesites and the Changing of the Guard at the Tomb of the Unknown Soldiers, I would allow, realistically, 90 minutes. So this, has you finishing at 6:10 pm. Assuming that you have to be at Union Station to pick up your night time monument tour, then that will take another 35 minutes to walk to the Arlington Cemetery Metro station and get to Union Station (assuming you don't have to wait at the Arlington Cemetery Metro station for a train.) So, you'd be ready to go at 6:45 pm which is 45 minutes before your stated meeting time of 7:30 pm. IF everything runs smoothly, it's possible that this could work for you. (To check walking times between places, I used Google Maps and to check the transit times on Metro, I used the Metro Trip Planner feature, which is a useful tool. It can be found at www.wmata.com)
Just a few other points:
1. There is a hop on/hop off bus at Arlington National Cemetery which makes stops at the Kennedy Gravesites, Arlington House (the home of Civil War general Robert E. Lee) and the Tomb of the Unknown Soldier. It also offers live commentary through other parts of the cemetery. This would not be a good idea if you are trying to visit prior to your night time tour on Tuesday, as you won't have time to ride around the cemetery. But if you come at another time, you might enjoy it.
2. I don't know what is included on the 6-hour tour on Wednesday, but I would imagine that a lot of it would be a re-hash of the evening tour that you did on Tuesday. You might want to skip the Tuesday evening tour and then just walk the monuments on your own Wednesday (or Thursday?) night. It's easy to do and there's plenty of threads on the Washington D.C. forum about how to best do it. (This would allow you more time to do the Arlington National Cemetery visit.) Or you could skip the 6-hour tour on Wednesday and use that time to visit more of the Smithsonian museums (there's a lot of them) or other places in D.C. such as the U.S. Capitol.
3. Finally, I've been to the Newseum twice (and it is a great museum). My first visit lasted 8 hours over two days (as the tickets are good for two consecutive days) and the 2nd visit lasted 6 hours. Expect to want to spend a lot of time there, especially if you are any kind of news junkie.
Edited: 2:48 pm, November 03, 2013