Before directory synchronization with Lync Online/Office 365 is used, this feature must be activated within the online tenant. Activating the feature is a one-time process and is as simple as clicking on a button within the online portal. However, the activation process can require up to 24 hours to complete. With that in mind, Lync Online administrators should plan ahead and activate AD synchronization several days before the AD user accounts need to be populated into the online directory.