Which type of speech is characterized by the absence of preparation time?

The type of speech characterized by the absence of preparation time is indeed impromptu speech. In an impromptu speech, the speaker is often given a topic and must respond with little to no advance notice or time to prepare. This type of speech requires the speaker to think quickly, organize their thoughts in real-time, and articulate them coherently.

Impromptu speaking is a skill that relies heavily on a speaker's ability to draw on their existing knowledge and articulacy under pressure. This spontaneity differentiates it from other types of speeches, such as extemporaneous speeches, which do involve some preparation and organization. Prepared speeches are planned and practiced beforehand, allowing the speaker to deliver their message with a level of polish and rehearsed structure. Informative speeches, while they can be prepared or extemporaneous, also do not align with the characteristics of an impromptu speech. Overall, the lack of preparation time is the defining feature of impromptu speeches.