Getting to Schiphol Airport

Since you asked, when I have a morning flight, I always book a hotel at the airport for the night before. I don't like surprises and don't want to have to deal with worrying about missed trains or long lines and so on. You really don't miss anything - you could stay in Delft until late afternoon and then get a train to the hotel and check in and relax.

Anyway, that's my philosophy - YMMV. :)

Dutch trains are very good about punctuality. Assuming you mean a transatlantic flight home - you don't say - you need to be at the airport at 7. It takes 38 or 39 minutes on the train. The 6:04 gets you there at 6:42; the 6:24 gets you there at 7:03.

On the off chance that there could possibly be a cause for going slow, I would choose the earlier one. It only stops at Den Haag HS, Den Haag Laan v NOI (the Laan van NOI stop has a really interesting name, a google search gives a really interesting story), and Leiden Centraal on the way. You will know you are there when the train enters a long tunnel and stays in it.

Have a dig around the official website - https://www.ns.nl/en

The flight home is trans- Atlantic.
The day prior to our departure we will be in Kinderdijk seeing the windmills and possibly spending a little time in Rotterdam on our way back to Delft. It may be too much to return from that, check out of our hotel on Friday evening and go to a new hotel for our Saturday morning flight. As long as the trains run, I would be willing to depart very early to ensure early arrival at the airport. I will definitely consider staying by the airport the night before a flight on future travels :)

I don't think you will need them, but there are even earlier trains available.

I would stay in Delft and take the early train same morning, assuming there is one at the crack of dawn. Try to save time at the airport. Check-in online ahead of time using your airline's app if you can. Having carry-on bags only would help too. Although I haven't been through it in a few years now, Schiphol is usually an efficient airport (last summer being an exception), and the Dutch trains seemed very reliable.

We had a really good experience with Dutch trains while we were there, until we tried to leave. I felt like I was in the song Hotel California, where you could check out but you could never leave. We were trying to go from den Haag to Stuttgart Germany. We were 10 mins on our train from den Haag to our first connection and the speaker came on and said there was emergency maintenance on the tracks and we would have to get off the train at the next stop. What was supposed to be three trains to Stuttgart ended up being 6 and we only made it to Dusseldorf and ended up renting a car and driving the 4 hours to Stuttgart. (The next ICE train from Dusselforf to Stuttgart was sold out)

I know it was a freak thing to happen, and the employees were super nice and helpful to get us back on track. I just don't know if I personally would risk a train ride in the morning for an international flight.

There is no need to move to an airport hotel. Taking the train from Delft to AMS is easy. I aim for the train that has me arriving at AMS 3 hours before departure (I have expedited security/check in privileges via Delta). That way, on the off chance a delay occurs, I have enough of a buffer with the unexpected delay (either the next train or a taxi). If you don’t have priority clearance at AMS, I would recommend taking the train that is scheduled to arrive at AMS by 7am.

Thank you all. I think I will stick with the original plan as they are not too far apart. Taxi was my back up plan in a worst case scenario.

I would advise keeping an eye on the Schiphol planner for flights - very helpful info about the expected chaos at the airport: https://www.schiphol.nl/en/my-travel-day/today It's updated frequently and is out about 3 weeks from today (but continue to check).

I failed to make a train from Brussels to AMS for a departure flight due to a train strike, so I personally would not be in transit on the morning of my scheduled departure. But others have offered good advice about how to make it go more smoothly.

"up renting a car and driving the 4 hours to Stuttgart. (The next ICE train from Dusselforf to Stuttgart was sold out)"

You didn't need to do that. Trains in Germany do not sell out, and you did in fact already have a ticket anyway.