I'll be taking Eurostar for the first time on an upcoming trip to London and Paris. I know we have to check in at least 30 minutes prior to departure, but I'm wondering if I need to plan for additional time, either at St. Pancras or upon arrival in Paris, to go thru immigration. I'm not trying to orchestrate split-second timing, just curious to know how this works. (And vice-versa, on the way back to London.)
I'm a US passport holder/US resident.
Thanks for any advice/perspective you can offer!