Does the number of daylight hours vary between Washington and other states in the 'lower 48'?
Yes...considerably! Miami (as of July 24th when I responded to this question) had 13 hours and 29 minutes of daylight, Los Angeles 14 hours and 2 minutes, Saint Louis 14 hours and 24 minutes; you see the increase in hours of daylight with increasing northerly latitudes due to the tilt of the earth in summer. Portland Oregon and Bangor Maine both receive close to 15 hours of daylight, while Seattle gets 15 hours and 19 minutes. I might add that hours of daylight don't always translate to hours of sunlight. Of course during the winter months, when the northern hemisphere is tilted away from the sun, the farther north you are, the fewer hours of daylight you'll experience.