Less than 24 hours in Stockholm...what are the must-see items?

Hop on hop off bus just as your mother likes after a long flight from Boise.

The day you arrive in Europe after a trans-Atlantic flight you walk not ride a bus unless you’re able to sleep on the way over. I know this from experience. Both of you will dose off and miss seeing the sights. Furthermore, by the time you go through customs, get from the airport to your hotel, check in and go to your room it will be time for dinner not a hop-on hop-off bus tour unless this is a night tour.

I would spend your first afternoon walking around Gamla Stan.
On the following morning (assuming you have enough time before you have to board), I’d head to the Vasa Museum as soon as it opens; you need at least 2 hours for this.

When you say arriving in Stockholm at around 2:20 PM. Do you mean arriving at the airport or is that an estimated time you'll be at your hotel?

We are anticipated to arrive at the airport at 2:20pm; we’ll be connecting from Munich.

If you land at 2:20, you still have to go through immigration and get to Stockholm.

Estimate you will actually get to your hotel sometime after 3:30 if you are lucky. (No immigration line and taking the Arlanda Express.)

My suggestion that late would be to explore Gamla Stan. Check to see if the Royal Palace will be open to visit.

Since you will have been on a very long series of flights, your best bet to fight jet lag is to be outside in fresh air and on your feet. A hop on hop off bus will lull you to sleep and most end by 4.

Depending on what time you have to check in for your cruise, you might consider doing the hop on, hop off bus the next morning.

Whatever else you do, I'd be sure to take one of the transit ferries. They're terrific, and you get a great view of much of the Stockholm archipelago from the water. Not expensive.

On the day of arrival, just walk through the winding streets and alleys of Gamla Stan/Old town (Österlånggatan being much less crowded than Västerlånggatan). For a soak in the rays of the setting sun, walk across the short bridge to Riddarholmen. In the morning: Walk to City Hall. Have fun!