Is it permissible to say "O Lord, may I see a black day for him," or is that considered cursing time?

Describing a day as "black" or similar is not considered reviling time. Therefore, it is not an act of reviling time to describe years as difficult, or a day as black, or months as inauspicious, because it is qualified. The Quran contains similar expressions, such as the verse: "in days of misfortune, that We might give them a taste of the punishment of disgrace." Thus, there is no objection to supplicating with this against those who deserve it.