Pat,
I doubt that there's much more than about a quart of
oil lost from the sump when the car is running. The only place it can be stored is in the valve covers, and when the
oil is hot it drains down pretty fast. The
oil galleries probably hold much less than a pint, and that takes quite a while to drain down.
When the oil is cold, all bets are off.
, so check the pressure when you rev the engine before the car has warmed up. The pressure won't drop to zero, but will be low as air is sucked into the oil pump.