According to Twitter, the new voice Tweet feature allows users to record up to 140 seconds of audio as their Tweet. To create a voice Tweet, the method is similar to a standard Tweet which is done through the Tweet composer.
If the feature is made available to you, there will be a wavelength icon next to the camera button. Even though the recording limit is 140 seconds, you can continue talking as Twitter will automatically create new voice Tweet and arrange them in a thread until you tap the Done button. At this moment, the voice Tweet is being rolled out to a limited number of Twitter users but will soon be made available to all Twitter users on iOS. However, the company did not reveal any availability info for those who tweet using Android or Twitter’s own website.