What a lovely part of the cosmos we inhabit for our photography. With soft light and cerulean tones, there is a magical moment in the clear-skied, pre-dawn blue hour when the light from our local star, in our tiny solar system's share of the universe, casts a sublime, relatively uniform luminance over everything. The dynamic range of the scene is agreeably compressed and balancing exposure is made easier. All these elements in combination reduce or eliminate the need for graduated filters or exposure bracketing. The relatively low light levels require slow shutter speeds which, in turn, produce smooth, misty water and soft cloud movement that add a little mystery to final results.
In my view, the pre-dawn blue hour really is the most uniquely rewarding and productive time for landscape photography (and, thankfully, most locations are totally deserted because the majority of the population is either still dozing or in their dressing gowns thinking about putting the kettle on).
Light and timing are two crucial elements of any successful shot and the blue hour magnanimously provides you with a synchronicity of both, offering up opportunities that are just as alluring as those of the golden hour.