Formal:
* À deux heures du matin. (This is the most literal translation and the most formal way to say it.)
Informal:
* À deux heures ce soir. (This is a more common and informal way to say it.)
You can also use:
* À deux heures dans la nuit. (This is another way to say it in a more casual way.)
Important Note:
In French, "du matin" (of the morning) and "du soir" (of the evening) are used to differentiate between times before and after midday.