In Azure AD Connect, the default synchronization interval is set to 30 minutes during installation.  In the majority of cases, 30 minutes is an appropriate balance between getting changes to Office 365 in a timely fashion, keeping the export set small enough to be effectively transmitted, and not overloading the on premises directories or Azure Active Directory.

The configuration of the Azure AD Connect synchronization schedule can be viewed using Get-ADSyncScheduler.

PS C:\> Get-ADSyncScheduler

AllowedSyncCycleInterval            : 00:30:00
CurrentlyEffectiveSyncCycleInterval : 00:30:00
CustomizedSyncCycleInterval         :
NextSyncCyclePolicyType             : Delta
NextSyncCycleStartTimeInUTC         : 1/23/2018 2:58:30 PM
PurgeRunHistoryInterval             : 7.00:00:00
SyncCycleEnabled                    : True
MaintenanceEnabled                  : True
StagingModeEnabled                  : False
SchedulerSuspended                  : False
SyncCycleInProgress                 : False

 

Administrators may adjust the synchronization interval using Set-ADSyncScheduler.  When administrators adjust the schedule manually this is reflected in the CustomizedSyncCycleInterval. 

PS C:\> Set-ADSyncScheduler -CustomizedSyncCycleInterval 02:00:00
WARNING: The sync interval you provided will only become effective after a sync cycle.You can choose to wait for the
automatic sync cycle to happen in next 30.00 minutes, or you can manually start a sync cyle by running
Start-ADSyncSyncCycle cmdlet.

PS C:\> Get-ADSyncScheduler

AllowedSyncCycleInterval            : 00:30:00
CurrentlyEffectiveSyncCycleInterval : 00:30:00
CustomizedSyncCycleInterval         : 02:00:00
NextSyncCyclePolicyType             : Delta
NextSyncCycleStartTimeInUTC         : 1/23/2018 2:58:30 PM
PurgeRunHistoryInterval             : 7.00:00:00
SyncCycleEnabled                    : True
MaintenanceEnabled                  : True
StagingModeEnabled                  : False
SchedulerSuspended                  : False
SyncCycleInProgress                 : False

When a synchronization cycle is administratively configured the value that is configured must be greater than the AllowedSyncCycleInterval.  In our example, the AllowedSyncCycleInterval is 30 minutes, therefore any customization must be greater than 30 minutes or it will be ignored.  A customized schedule cannot be created less than the AllowedSyncCycleInterval.

PS C:\> Set-ADSyncScheduler -CustomizedSyncCycleInterval 00:15:00

The value for the customized sync interval is lower than the allowed value.
Requested new interval = 00:15:00  Allowed interval = 00:30:00
Scheduler will still run at the allowed sync interval even after successful execution of this cmdlet.

Are you sure you want to continue?
[Y] Yes  [N] No  [S] Suspend  [?] Help (default is “Y”): y
WARNING: The sync interval you provided will only become effective after a sync cycle.You can choose to wait for the
automatic sync cycle to happen in next 30.00 minutes, or you can manually start a sync cyle by running
Start-ADSyncSyncCycle cmdlet.

In recent days, some customers have reported that the AllowedSyncCycleInterval was set to 2 hours even though the default should be 30 minutes.  Here is an example…

AllowedSyncCycleInterval            : 02:00:00
CurrentlyEffectiveSyncCycleInterval : 02:00:00

CustomizedSyncCycleInterval         :
NextSyncCyclePolicyType             : Delta
NextSyncCycleStartTimeInUTC         :
PurgeRunHistoryInterval             : 7.00:00:00
SyncCycleEnabled                    : True
MaintenanceEnabled                  : True
StagingModeEnabled                  : False
SchedulerSuspended                  : False
SyncCycleInProgress                 : False

The AllowedSyncCycleInterval is not administratively configured.  If this value is not administratively configured then how did the value automatically change?

Azure AD Connect is a client of Azure Active Directory.  The AllowedSyncCycleInterval is determined through the clients connection with Azure Active Directory.  There could be some instances where this value may change.  For example, if an Azure AD replication partition becomes behind the service may back off the synchronization interval of Azure AD Connect.  In this instance, the value was adjusted through the server side policies controlling sync intervals.  When any service issues are rectified, the value automatically reverted to default.

The effective sync cycle is determined as a combination of the AllowedSyncCycle and the CustomerizedSyncCycle.  For example if the CustomerizedSyncCycle is greater than AllowedSyncCycle, the CustomizedSyncCycle will take precedence.  In this instance, most customers noted that the AllowedSyncCycle was greater than the default and any attempts to set CustomerizedSyncCycle to default were ignored since the value was lower than allowed.

When the allowed changes, you are encouraged to open a case with customer support services for review and confirmation.  Should the administrator require synchronization at intervals lower than the allowed, it would have to be accomplished through manual synchronization.

Information regarding the AD Connect sync scheduler and manual synchronization can be found here – https://docs.microsoft.com/en-us/azure/active-directory/connect/active-directory-aadconnectsync-feature-scheduler.

From the MS blog https://blogs.technet.microsoft.com/timmcmic/2018/01/23/office-365-adconnect-synchronization-interval-changed-automatically/

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