No worries Plaidmoon! Amsterdam does Daylights Saving too.
DrRox was right, teams did seem to arrive in two waves. Here are the tweets the times of which I managed to find (can't find the Facebook sightings lost in the depths of time, nor the one with a picture of the twins):
"So cool! The #AmazingRace is filming at Central Station in Amsterdam as one of their stops." - SNKRFRK
"Just seen a crew from the amazing race USA zoom passed us - they asked us for directions we were like "sorry" hahahaha" - goodlucklive
"Spotted an Amazing Race checkpoint box right in front of the station o_o what if i steal a ticket~" - zerachel
"UWOO 2 guys using similar shirts+backpacks just walked by the cafe..AND I thnk one carried an AA (sic, "AR") ticket!!!" - zerachel
"At Restaurant De Roode Leeuw Brasserie, Amsterdam~ chilling while eating bitterballen :3" - zerachel
"So the Amazing Race has just been spotted in Amsterdam! Good luck team!" - toryalmond, with Josh/Brent and Abbie/Ryan
"An Amazing Race team literally ran into us in Amsterdam today #mylifeiscomplete" - mpetroff
We'll tackle this in two parts. First let's consider the possibility that they just touched down in Schiphol and took the train downtown. Working backwards on the trains, that means they left the airport at 12.09pm and 3.59pm latest. Taking a minimum of ten minutes to disembark and get to the trains at Schiphol, that means we are looking for flights landing no later than 11.59am and 3.49pm respectively.
This doesn't jive with any of these cities close enough to Moscow to warrant just a one-day leg:
Moscow (arriving 6.58am, 12.31pm)
St Petersburg (arriving 8.53am, 7.35pm)
Tallinn (arriving 8.56am, 7.48pm)
Riga (arriving 1.00pm, 7.05pm)
At this juncture, I'd take a leap and say that Leg 8 is neither in Russia nor in the Netherlands. (Fingers crossed!) For the former, flights just don't arrive at the right times. For the latter, trains from anywhere in the Netherlands to Amsterdam should be frequent, at the slowest two an hour in the daytime. Unless there were other semi-bunching mechanisms in place or unless there were unseen racers arriving at other times, we shouldn't be seeing two distinct waves of racers, arriving almost four hours apart.
Ignoring connecting flights, here are the cities with pairs of flights arriving at the appropriate times:
Zurich, Bucharest, Gothenburg, Bremen, Nuremburg, Paris, Munich, Milan, Stavanger, Rome, Frankfurt, Stockholm
But if we take away the cities with alternative flights in between the pairs, we're left with:
Bucharest, Bremen, Nuremburg, Stockholm
I don't think Bremen and Nuremburg are the kind of city (or at least airport!) TPTB likes to use, and Bremen's close enough to the Netherlands that a train might have been better for production. So going by this, good suspects look like Bucharest and Stockholm.
But wait! Notice the list of cities close to Moscow? It doesn't include Vilnius in Lithuania; Vilnius doesn't have direct flights to Amsterdam on 11 Jun. But when you consider the quickest ways to get from one to the other, you get:
Vilnius via Frankfurt to Amsterdam, arriving 9.49am (scheduled 0600-0715, 0855-1005)
Flight via Prague scheduled 0525-0605, 0910-1045 (Frankfurt is preferable)
Flight via Moscow SVO scheduled 0540-0805, 1105-1215 (Frankfurt is preferable)
Vilnius via Copenhagen to Amsterdam, arriving 11.27am (scheduled 0640-0710, 1010-1135)
Vilnius via Kiev to Amsterdam, arriving 11.44am (scheduled 0705-0835, 0940-1135)
Vilnius via Helsinki to Amsterdam, arriving 3.21pm (scheduled 1145-1255, 1400-1530)
Vilnius via Bremen to Amsterdam, scheduled 1010-1100, 1500-1600 (Helsinki is preferable)
Which makes Vilnius a good candidate as well.
What about the train option? I'm not sure how to approach this problem. You guys have a clue?