I have a 616AM outbound train from London to Amsterdam. It is a Eurostar Standard and my ticket says to arrive by 5:01 AM. I thought I needed to be there earlier for security. What time should I really be there by? TIA
Go by the time shown on your ticket. That is your official time to enter the Eurostar area for security and immigration.
75 minutes is the current recommended time. It was longer until a few months ago.
They could open your boarding line earlier than 5:01, but you'll stand in a queue until they actually open the security check for your train. Since you're there at the start of the day and I think there are only a couple early trains at that time I doubt they'll open it much earlier than 5. At least there won't be as many people milling about waiting for the many mid-day trains which can make the main part of the train station a little crazy.
If you need coffee, I think only Starbucks is open that early, not sure about what might be open after security. Ordinarily I'd suggest grabbing breakfast at the M&S right next to the Eurostar boarding area but it doesn't open until 6, so maybe pack up something the day before.
Arrive at the time given on your ticket. Usually lines are short for the early morning departure (my experience from 2023). Also, figure out how you are going to get to the station at 5am. Don't assume the same tube service that you would have later in the day. I made this rookie mistake and found out that my tube station did not open till 15 mins later than the tube I planned to take...fortunately I had built in a buffer but it led to some interesting conversations with the street sweeper and the station superintendent. Enjoy your trip!