In the smart grid, time information has evolved from a means of relating historical data post-fault to enabling real-time analysis and immediate remedial action, supporting, eventually, automated operations [11]. The accuracy requirements for time synchronization vary by application, ranging from seconds to microseconds across different grid functions [12]. For instance, the timing precision for phasor measurement units (PMUs) is significantly higher than for supervisory control and data acquisition (SCADA) systems. Beyond accuracy, the availability, backward compatibility, and security of time synchronization systems are also critical considerations, with various standards defining the specific requirements for different grid components and devices [13]. Precise time synchronization is essential for maintaining the stability and reliability of modern smart grids [14]. Accurate synchronization accelerates a broad range of smart grid operations, such as fault detection and network clearing, synchrophasor measurement to monitor network stability, sequence of event time stamping, data acquisition, demand side management (DSM), differential protection, frequency deviation measurements (FDM), and smart metering synchronization. The importance of time synchronization extends to the security of smart grids. Time synchronization attacks (TSAs) pose a significant threat to the precise functioning of phasor measurement units (PMUs) in the context of smart grids [15]. Many operations in power grids, such as fault detection and event location estimation, depend on precise timing information. Therefore, precise time synchronization is not only a technical requirement but a cornerstone of the smart grid's ability to deliver reliable, efficient, and secure power. As the grid continues to evolve with the integration of renewable energy sources and advanced technologies, the role of accurate time synchronization becomes increasingly critical. Time synchronization in power grids is achieved through various methods. While some techniques have been in use for decades, others are recent innovations. The structure of a time synchronization system typically comprises two key components: the time source and the time distribution system. The most widely used time source in power grids is the Global Navigation Satellite System (GNSS) [16], which provides timing accuracy within one microsecond [17], ideal for protection and control applications [18]. The time distribution system, on the other hand, is tasked with aligning the clocks across network nodes to match the time source, thereby ensuring synchronized operations with the required accuracy [19]. The Network Time Protocol (NTP), for example, is widely implemented and provides timing precision within tens of milliseconds [20]. However, the 2016 GPS malfunction, which offset timing signals by 13 microseconds, highlighted the vulnerability of solely relying on GPS, as systems requiring precise timing, such as communication networks and power grids, were significantly disrupted [21; 22]. This incident underscored the need for robust backup systems to mitigate future risks and ensure infrastructure reliability. Emerging techniques for time synchronization are increasingly being developed, yet they lack comprehensive documentation within the existing literature. This survey aims to fill this gap by offering a thorough review of current time synchronization mechanisms. The main contributions of this paper are as follows:  
* A comprehensive overview of time requirements across various power grid applications, detailing the specific timing demands of different devices. * A comparative analysis of time sources and distribution mechanisms, covering both established and emerging approaches with a focus on power grid applications. * A multi-dimensional assessment of implementing new time synchronization techniques, evaluating performance and feasibility in power grid contexts. This paper introduces novel perspectives on time synchronization techniques, emphasizing their applicability in smart grids.