System Configuration : Preferences : Synchronization Preferences : Synchronization Section

Synchronization Section
Minimum Sync Delay
Sets the initial amount of prime time (in frames) your system’s devices need to achieve synchronization “lock.” This amount varies for each device. Pro Tools lock up delay is set by entering a value for Minimum Sync Delay in the Synchronization page of the Preferences. The lowest value available is 15 frames. Find the shortest possible lock-up time that your equipment can operate at consistently, and set this as the Minimum Sync Delay. On systems using MachineControl, enabling the Use Serial Timecode option will make machines lock up much faster. (Serial timecode requires both a qualified synchronization peripheral and external devices to be locked to house video reference.)
Delay Before Locking to Longitudinal Timecode (Avid HDX, Pro Tools|HD, and HD Native Systems Only)
Sets the amount of time (in frames) for Pro Tools to lock to incoming LTC. Use this option when locking Pro Tools to a stable timecode source (such as a non-linear tape machine or LTC generator) and not a linear tape machine.
Delay Before Locking to Serial Timecode (Avid HDX, Pro Tools|HD, and HD Native Systems Only)
Sets the amount of time (in frames) for Pro Tools to wait before attempting to lock to machines that issue servo lock messages. This setting allows time for the servo mechanisms to achieve stable lock.