Data stream processing is built on the core concept of time. However, understanding time semantics and reasoning about time is not simple, especially if deterministic processing is expected. In this talk, we explain the difference between processing, ingestion, and event time and what their impact is on data stream processing. Furthermore, we explain how Kafka clusters and stream processing applications must be configured to achieve specific time semantics. Finally, we deep dive into the time semantics of the Kafka Streams DSL and KSQL operators, and explain in detail how the runtime handles time. Apache Kafka offers many ways to handle time on the storage layer, ie, the brokers, allowing users to build applications with different semantics. Time semantics in the processing layer, ie, Kafka Streams and KSQL, are even richer, more powerful, but also more complicated. Hence, it is paramount for developers, to understand different time semantics and to know how to configure Kafka to achieve them. Therefore, this talk enables developers to design applications with their desired time semantics, help them to reason about the runtime behavior with regard to time, and allow them to understand processing/query results.