Checked Luggage with LONG layover

For question #1, it really depends on the airline policy. Some airlines don’t permit short checking. Others require you to pick up your bag if the layover is overnight and/or exceeds a certain duration. I think you will need to contact KLM and find out if you can check your bag just to AMS. If they don’t allow this, you will need to plan to pack an overnight carry-on bag.

There is direct train service from Schiphol Airport to Leiden many times per hour. The standard 2nd-class fare is 7.30 euros. The travel time is 16 to 21 minutes; some trains don't even make intermediate stops between the airport and Leiden.

I have no personal experience with staying near Schiphol, but zooming in on Google Maps shows several hotels on the property--Hilton, Sheraton, Citizen M and Yotel. There are probably reviews for all of them on booking.com, though reservations made on the corporate websites are probably less expensive.

I think you have more options here than you may realize, given the relatively short trains.

For starters, how much stuff do you need for one night? Pack what you need into a carryon
and let the checked bag(s) sit in Schiphol for the night.

At check-in in Zurich is where you need to make sure your bag is tagged only to Amsterdam,
if that's what you have to do. Otherwise, if you want them to retrieve it, it will take forever.

Waiting to retrieve bags, then storing them someplace or checking into a hotel on-airport,
will use up a couple of hours of your sightseeing time.

Given that it's a 20 minute train ride to Leiden, just go there and spend the night. The hotel
is probably cheaper than an on-airport hotel at Schiphol, and you'll have more choices.

Unless your flight out of Schiphol to the US is at the crack of dawn, which transatlantic flights
usually aren't, you should be able to still get back to the airport with 2-3 hours to spare so
you can check your bags again, if that's how it ends up.

From my experience, airlines will generally will not allow you to get your bags unless this is a stopover (I.e. the layover is greater than 24 hours). If you can’t get your bags, it is worthwhile the next morning to go to the airline counter to make sure your bags get loaded onto your flight home since it will have been sitting in some holding area overnight.

I should clarify, I'm really asking if they'll let me just check it at Zurich to Amsterdam and then pick up at baggage claim. I don't mean could I retrieve it out of some cold storage. I think the layover will be over 24 hours, so it's probably an option, as it likely falls in the stopover category. Just wondered about anyone else's experience. In all our travels, we've never had a stopover.

We head out early the next morning, so we may just stay at the airport, not Leiden but excited to have unexpected time to see Leiden.

Appreciating everyone's responses!! Thanks!

My earlier response was addressing just your situation- I.e. checking your bags just to AMS. If your connection is over 24 hours, then the airline will likely only check you in to AMS and you will need to recheck in the next day again.

That said, most of my experience is with Star Alliance carriers. Some of the other carriers may have different rules.

I think the layover will be over 24 hours

Your initial post said 20+ hours. Is it more than 24 or less than 24. You need to know precisely how long the layover is (based on the time the flight is scheduled to land at AMS and the time it is scheduled to depart) and you need to find out specifically ewhat KLM’s policy is. I checked their website but did not see the info. You might try asking on flyertalk.

Again, each airline has it’s own policy. Some airlines only allow you to short check when the layover exceeds x hours (e.g., 24 hours or 12 hours are some of the policies that I have seen). Some airlines do not allow you to short check.

Corrected my typo on time layover/stopover (oops, sorry for the confusion.)
Appreciate the thoughtful responses!