Two contrasting experiences for me.

February 28th, BA113 arrived at 7:30pm in F, so off the plane quickly and we stood in the queue for at least an hour. In fact we stood in the corridor for most of it, once we made it into the immigration hall, we were processed pretty quickly. Allegedly, the CBP shift hadn't turned up!

Two weeks ago, BA117 arrived about 25 minutes late on Saturday 9th November at midday. I had a connection in T8 and was worried after last time, so myself and 2 others, who had even shorter connections asked to be off the plane first. I was sitting in the TO AA Flagship Lounge at 12:25 with a glass of wine in hand. And that included chatting to the CPB agent for a few minutes as to why I only had $0.28 on me and what would happen if the ATM's went down!

So timing or just luck, I don't know.