Satellite networks (SNs) have emerged as a key enabler to provide global, ubiquitous and seamless Internet of Things (IoT) services in a flexible and affordable manner. Different from conventional delay-tolerant tasks, many intelligent IoT services are delay-sensitive, requiring scheduling methods to make fast decisions on dynamic computing and communication resource allocation. However, existing satellite networking technologies adopt store-carry-forward data transmission mechanism, and ignore the timely processing requirements of IoT applications, which can incur unacceptable latency and is not applicable for delay-sensitive scenarios. This article investigates the time-deterministic networking strategy for real-time IoT applications over SNs. We first introduce the overall satellite-based IoT architecture, and discuss its key technologies in terms of time-varying network representation and time-deterministic routing. We construct the time-varying graph to precisely depict dynamic topologies, diversified functions, computing and communication resources and resource reservations in SNs by designing the enhanced snapshot division mechanism. Then, we propose time-deterministic routing schemes for both the on-satellite computing IoT applications and data-intensive IoT services, and provide corresponding evaluations. Finally, we discuss the future research directions of the satellite-based IoT.