Mike - I would suspect the check valve - logically - it makes sense. If the valve has a slow leak it would take about 8 hours to lose enough pressure to cause the car to crank before firing. I have an old Olds with a V8 and 4 barrel carb on it - the carb has an internal leak that causes the fuel to drain out overnight that causes the car to crank 10 times before starting in the morning -the rest of the day it starts first crank. With the fuel pressure dropping on your car after 8 hours - the check valve seems a good culprit. The accumulator normally acts up when the car is hot and you cannot get enough fuel pressure for it to run properly until you get it to rev a couple of times. I know because mine was bad. Even though it started cold perfectly - it was a nightmare getting it to stay running when first started hot. I would say go for the check valve first.