Four Day Itinerary

Day 1 is very doable. If you land at 9:00 a.m., strong odds you'll be to your AirBnB before noon. Little Mermaid is really disappointing. Note that the Torvehallerne closes as early as 5 p.m. on certain days, and is only open as late as 8 p.m. on Friday. Might be a better lunch place. It is great though, definitely get there.

Day 2 - we found Christiansborg to be the least interesting of the palaces in the city. That's just my opinion. Copenhagen Street Food is awesome - if you have time and it's a nice day, sit outside on the canal and have a few drinks and people watch. We really loved it. Rosenberg is great. You'll almost certainly have time to do more that day, especially with an early start.

Day 3 - again, I think you'd have time to do more. National Museum is fantastic. City Hall won't take very long. Carlsberg is fun if you like to hang out and have a few beers, but it isn't the most impressive brewery tour by any stretch.

Day 4 - sounds like you'd want to do maybe Hillerod or Helsignor. If you do the latter, stop at the Louisiana Museum of Modern Art on your way back to Copenhagen. It's excellent and on the same train line.

If it were me, I might try to hit the National Museum on Day 2 in the place of Christiansborg in the morning, and on Day 3, head to Roskilde or Hillerod for part of the day. You'd still have time to go to Carlsberg in the afternoon.

Thank you Steve! I'm glad you think I will be able to fit in more during the day. I would like some time to sit at a café or along the canal with a drink and some food. I don't plan on going into Christianborg Palace, but I would like to go up in the tower if I'm there early enough and there isn't a long line. Day 4 I plan on taking a tour through Viator to visit Krongberg Castle, Fredensborg Palace, Frederiksborg Castle and town of Elsinore. I was going to plan a day trip out on my own through public transportation but my 72 hour Copenhagen Card will have expired by then.

How much time did you spend in Rosenberg? I went to London last summer and really enjoyed seeing their crown jewels.

Rosenborg Castle doesn't take very long...90 minutes is more than enough time. It's quite small but well worth seeing...the crown jewels in the basement are really nice - not quite the opulence of the Tower of London but still beautiful!
My opinion is that the National Museum is that it's worth your time. They have some interesting rooms of Danish masters that are very nice! Some of the paintings are quite humorous and really give insight into the Danish soul. Lots of minor paintings by well-known names in the impressionist room. If you like modern art then they have a whole wing of it!
Although the Little Mermaid seems like the obligatory stop, it's pretty silly. It's small, very out of the way, and not in that nice of a setting.
You'll be at your Airbnb well before 12. It's a very short ride from the airport to town whether you're taking public transport or a cab.
I think your itinerary is very workable!

We did a great day trip tour that included the Viking Museum and a couple of castles away from the city. It was great.
We did a Free Walking Tour that was great. Also, recommend a canal cruise.