When referring to a difficult or challenging time, the phrase "dark hour" is often used. However, there are many synonyms for this phrase that can add some variety and depth to your writing. Some examples of synonyms for "dark hour" include "troubled time," "difficult period," "time of crisis," "hour of adversity," and "time of hardship." Additionally, you could use more specific phrases that refer to certain situations, such as "time of grief" or "hour of despair." Choosing the right synonym can help your writing to be more precise and engaging, while still conveying the same meaning as the original phrase.