Why dinner is at eight

Full dark in core season arrives between 19:40 and 20:10. Human dark adaptation takes about thirty minutes to become useful and around two hours to complete, and a single glance at a phone resets most of it.

So dinner starts when it is already dark, in a room lit low and red, and ends at the point where your eyes have done the work without you noticing. Walk out at ten and you are already adapted. Walk out at ten having eaten at six under white light and you have wasted the first hour of your night standing in the dark waiting for your own retinas.

This is the entire explanation. It gets described as a philosophy in most write-ups, which we have stopped correcting.