Praise be to Allah, and peace and blessings be upon the Messenger of Allah. To proceed:
There is nothing wrong with making this supplication, and it is not considered cursing time, because what is intended is to ask Allah to bring upon aggressors or wrongdoers a severe day of punishment and defeat, not to insult the day or time itself.
The Quran describes certain days as severe, as Allah says:
“This is a distressful day.”
And He, Glorified and Exalted, says:
“On a day of continuous misfortune.”
This is a description of what occurs on that day, not a condemnation of time itself.
What Does It Mean to Curse Time?
Scholars have explained that cursing time occurs when a person condemns or insults time because of the calamities that occur during it, while Allah is the One who controls and decrees all affairs.
However, merely describing a day as severe, or supplicating that a day be severe upon wrongdoers, does not fall under this prohibition.
Conclusion
Supplicating by saying, “O Allah, make us witness a dark day for them,” is permissible and is not considered cursing time, because what is intended is to ask Allah to make that day severe upon the wrongdoers, not to condemn time or object to Allah’s decree.
And Allah knows best.