A casual 30-45 minutes. Be sure and park in correct area. Take elevators or escalators as required. Food, snacks and beverages are available. It's a beautiful building.
I'd arrive about 30 minutes ahead of time, 45 minutes or so if it's your first visit.
The train wont leave before its scheduled time to depart. I like to arrive 30 minutes before the scheduled departure time. This gives me time to purchase a ticket and find the track to which my train is train is traveling on.
No less than 30 but if you're a risk taker, fly in 10 min before
Around 30 minutes is ok
Conservatively, I'd allow 10 minutes to buy tickets (if you don't have them already) and another 15 to make your way to the track.
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