This paper investigates the time synchronization aspect of transmission scheduling in an optically groomed data center network (OGDCN). The architecture is based on a hybrid optical-packet approach and uses broadcast domains and wavelength division multiplexing for communication. The salient feature of this architecture is that all network paths are readily available in the optical domain and there is no need for optical path establishment. A source-destination pair must tune to a predefined wavelength at a scheduled time during data transfer. Every compute and storage node (CSN) is equipped with one or more tunable optical transceivers. As with any broadcast network, multiple transmitters that share a link segment cannot use the same wavelength on a link at the same time since this would result in collisions. Hence, transmission scheduling is required to prevent collisions and to allot an exclusive time duration for every transmission request. This paper's focus is on the time synchronization aspect that is critical for scheduling. Two schemes - continuous and discrete (slotted) time - are defined and evaluated. The objective of this paper is to understand the various factors affecting performance of these synchronization mechanisms. With the former scheme, clock accuracy has a significant impact on performance. With the latter scheme, propagation delay variance and packet length distribution impact performance in terms of utilization. The paper presents an evaluation of the performance of these mechanisms in the context of the OGDCN architecture. The results show that continuous time is able to better efficiently utilize network resources. © 2016 IEEE.