Flight leaves Frankfurt at 10:15am

That is more than adequate. Technically that is a domestic flight so two hours is adequate. Also the airport tends to be slower at that time of the morning. And the Germans tend to be fairly efficient.

2 1/2 hours should be plenty of time. I'd be worried about some hiccup in the rail system that could slow you down. What day? I'm seeing 7:59 arrival at FRA. Assume you are talking about St Goar.

I saw 6:19 and 7:34 for three weekday dates I checked in Apr, May, and June, but double check your date. On a Sunday the first train was an 7:19 (8:34 arrival).

I flew out of Frankfurt on NWA before Delta bought them. I stayed in Mainz. The airline recommended I get there 3 hours ahead of departure time. I was probably only 5 or 10 minutes later than that. When I got to the check-in there was a really long line. They only had two people to check in an entire 747, and they stopped all economy check in whenever someone from 1st class arrived at check in. It took me over two hours in line to check in, but in that time very few people arrived behind me, so I could have arrived an hour before departure and still made it. BTW, I had only carryon luggage, so no checked bags to make it to the plane.

Delta uses Terminal 2, which is farther from the train stations, so it will take time to get up to the Sky Line and back down.

I think that would be plenty of time, but if you decide not to risk it, I would recommend you stay at Hotel Königshof, in Mainz. The hotel is right across the Bahnhofsplatz from the Bahnhof - a few minutes walk. There is an S-Bahn at 7:03 that gets to the airport at 7:29. They have a great breakfast buffet.

You'll go through security in Frankfurt, but if you change planes in Amsterdam, you go through Schengen emigration there.

Thanks Lee. Our departure date is Monday 30 May, so I think I've got my train times right. I was thinking it should be enough time but it doesn't leave much margin for error or unexpected delays. St Goar is our location, (autocorrect got me). I've heard some say three hours prior to departure, but that seems excessive. Of course we could always move for our last night, but that not that convenient either. Minneapolis has had much publicity lately about the understaffed TSA and reconfigured checkpoints causing painful delays so I'm just a little nervous about it.

OK, you also have a connection at 5:19 that will get you there one hour sooner. There is also back-up with a regional express at 6:45 that is direct arriving 8:05 which should still be alright.