As of my last knowledge update in September 2021, WHMCS does not have a specific setting for configuring the sync frequency for pending domain transfers. The synchronization of pending transfers in WHMCS is typically managed through the domain registrar's integration settings.

If you're using a specific domain registrar with WHMCS, I recommend checking the registrar's documentation or support resources for information on how they handle synchronization of pending domain transfers.

Keep in mind that the process and options may vary depending on the registrar you're using and how it integrates with WHMCS. Always refer to the specific documentation provided by your registrar for accurate and up-to-date information.