Twilight for Twitter on iOS is now available for IOS. The Night Mode feature was first made it to Twitter for Android back in June. Enabling night mode in the app just changes the colors from the bright default white and black text to a dim grey scheme.
Night Mode in Twitter for iOS needs to be toggled on and off manually, as there's no way to make it automatically enter this state in the evening and then get out of it in the morning. Still, it's clearly useful to have.
Twitter confirmed this in a tweet also.