It is generally safe to eat an orange at night, but it's important to keep in mind that citrus fruits like oranges are high in vitamin C and can be acidic, which may cause some people to experience heartburn or digestive discomfort if eaten too close to bedtime.
If you are prone to acid reflux or indigestion, it may be best to avoid eating citrus fruits or any other acidic foods in the evening. However, if you do not experience any negative effects from eating oranges at night, there is no harm in doing so.
It's worth noting that some people believe that eating fruit before bedtime can interfere with sleep due to the natural sugar content, but there is no scientific evidence to support this claim. In fact, eating a small snack before bedtime that contains carbohydrates and protein, such as a slice of whole grain toast with almond butter or a small bowl of low-sugar cereal with milk, may actually help to promote better sleep. Ultimately, the best approach is to listen to your body and eat in a way that makes you feel your best.