Blue hour gives you a changing balance between sky brightness and artificial light. Early in that transition, a lamp may look modest against the sky. Later, the same lamp can dominate while unlit details become difficult to record. Watch that relationship in your frame and make photographs as it changes. The period you can use depends on the location, season, weather and the kind of image you need.
Use the 3D artwork Blue Hour as a reference for color and atmosphere before a photography session. Once you are on location, compare the brightness of the sky with the lights that appear in the composition. That balance determines when to make the frame.
Arrive with the composition mostly solved
Choose the camera position while there is enough daylight to assess the route and foreground. Check that you can remain there without blocking access. If you plan to use a tripod, confirm it is permitted and leave safe space around its legs. Establish the frame before the balance of light starts changing quickly.
Make a test image with more sky than you expect to keep, then one with less. The amount of sky in the composition changes both the visual balance and the meter reading. Decide whether the sky is the subject, a source of separation behind a person, or a small part of an architectural scene.
Use sunset or twilight information to plan arrival, while allowing for local obstructions. A ridge, building or thick cloud can change the light you see well before an open horizon would. There is no single number of minutes after sunset that guarantees the same appearance everywhere.
Choose exposure around movement
For a stationary scene, a stable camera can allow a longer exposure as daylight fades. Set an aperture that gives the depth of field you need, then lengthen shutter time as appropriate. Inspect moving leaves, water or people in the frame. Their blur may become a useful part of the photograph, or it may conflict with your intention.
A portrait needs a different compromise. Even a person who is trying to stand still moves slightly. Choose shutter speed for that movement and increase ISO if the light no longer supports it. A tripod can hold the camera steady while the subject still blurs. Check the eyes at a useful magnification after a short sequence.
At any exposure, inspect bright lamps and lit signs. A small clipped bulb may be acceptable; a large blank area across the subject or an important building detail may change the image. Reduce exposure for a test and compare what happens to the shadows. If the brightness range is too large, adjust the composition or choose an earlier stage of the evening.
Keep useful color separation
Automatic white balance can change the apparent color between frames as the sky darkens or as artificial light fills more of the composition. A fixed setting gives you a consistent reference while comparing a sequence. Raw capture allows more flexibility later, though it cannot recover every clipped color channel or detail lost to exposure.
Set white balance according to the part of the scene you want to treat as the reference. Correcting a warm lamp toward neutral can make the sky appear more strongly blue. Warming the entire image can reduce that difference. Neither choice is compulsory; inspect skin and neutral surfaces as well as the sky when deciding.
For a portrait with different light on each side of the face, a global adjustment may leave an uneven color split. Move the person toward one main source or accept the split deliberately. The Night Portrait Series provides another visual reference for considering color in a darker setting.
Repeat a frame as the balance changes
Keep one composition long enough to compare different stages of the evening. Make a photograph, note the exposure and repeat after the scene has visibly changed. Adjust only what the fading light requires. This makes it easier to see whether a stronger result came from darker sky, brighter-looking lamps or a different camera choice.
Review focus again after changing the composition. Low contrast can make autofocus less reliable, and a bright distant lamp may attract focus away from a face. Use a focus area appropriate to the subject and verify the result. If you focus manually for a stationary scene, inspect a magnified preview before making the longer exposure.
Stop extending shutter time when it changes a moving subject beyond what you want. At that point, raise ISO, use a suitable wider aperture or change the photograph you are making. Record the last usable settings and composition in your notes. On a future visit, those notes help you reach the promising position before the sky and lamps reach a similar balance.