User Configuration > Administrative Templates > Skype for Business 2016 > Microsoft Lync Feature Policies
User
HKCU\software\policies\microsoft\office\16.0\lync
When set, this will delay the initial download of the Global Address Book by a random number between 0 and the number of minutes specified after sign-in. When the value is 0, the download will begin immediately after sign-in. By default, the value is 60. This means that there will be a random delay between 0 and 60 minutes after sign-in before Lync begins to download the address book.