At the Summer Solstice, the Sun arrives at a declination of +24.5 degrees in the sky. This means that at the North Pole, the elevation of the Sun above the horizon reaches a maximum at at elevation of 24.5 degrees above the southern horizon. It is the Arctic day at all hours of the day. This lasts from the Spring Equinox to the Autumnal Equinox. After that, the Sun never makes it above the Arctic horizon and you have 6 months of night. In the Northern Hemisphere, there are no times in the Summer when you have perpetual twilight conditions, however, you can have the 'evening Sun' effect late in the evening as you approach the Arctic circle near latitude 66 degrees.