From day to night
Once you’ve created an effect like this it’s easy to go from day to night. First, add a Gradient Map adjustment layer (as in Step 1) and then customise the gradient so that the blend goes from black to dark blue (try #455E78 here). Next, fine-tune the lightness of the image using a Levels adjustment layer until it looks suitably moody. Finally, hit Ctrl/Cmd+Shift+Alt +E to merge a copy of all the layers, then grab the Burn tool, with Range set to Midtones and Strength at 20%, then paint to darken down the foreground, gently hiding the details that would naturally be in near-darkness.