If Amtrak were truly concerned about dining car profitability, given its formidable fixed operating costs (primarily staff who are paid for the duration of the train's run), you'd think they'd move heaven and earth to have the dining car open for business during as many hours as possible--especially hours that folks consider normal meal times. I understand that the kitchen needs to be cleaned, restocked etc. But the only way to make sales is to be open for business.
I think about this every time I'm on a LD train where the diner shuts down 1-2 HOURS before its arrival at final destination.