UK to Schengen to USA, when to be at the airport? [closed]

this is mostly a non-issue but anyway.

I will by flying from BHX to ORD via AMS next week. I have ample layover time in AMS but my flight from BHX departs at 6:10am. Both flights are booked on the same ticket, both with KLM. I will travel only with carry-on luggage and will check in online if possible.

How early do I need to be at BHX for the "non-transatlantic" leg? I'm asking as I'm not sure when the screening/pre-immigration for the US will take place, at AMS or at BHX. I cannot see how it could possibly happen at BHX, but you never know.

If anyone has any experience with this kind of itinerary (UK-Schengen-US), kindly let me know. I don't fancy getting to the airport at 3 o'clock, but of course I also don't want to be denied boarding because I arrived 60 minutes before departure. Any help is appreciated. Cheers!