Originally Posted by
aumarosa
Late to this question but curious because I am sending my 80+-year-old mother on a similar route, how much time did clearing US customs take (or does it usually take)?
It is difficult to say. My last transfer to the transborder terminal (gate D5 to the transborder MLL) took about 20 minutes. That includes walking, security and US CBP. It was Sunday, noon-ish. But YMMV. I've seen much worse.