I'd argue the point about it being too dark to fly just after sunset. I did most of my training in the last slot of the day at our airfield - 7pm to 8pm, and it was the frustration of having to land when it was such a beautiful evening that made me promise I'd get the night qualification. Often I'd drive home after the lesson and not have to turn on the car headlights until an hour after sunset. This time of day always seemed the most relaxing and beautiful time to fly for me, so when I finally get the qualification, it'll be for the reasons Bertie mentions.
In June, at 53deg North, on an ideal clear evening, I reckon you could fly until around 21:30 or 22:00 and still (just) be able to see to make a forced landing. In fact, the vis always seemed better just after sunset, as you'd lose all that glare from the low sun.