By default AD Connect automatically syncs to Azure AD every 30 minutes. Although this works fine in most companies, it could be considered too long a period if there is a high rate of change within an organisation.
To alter the default sync period use Powershell
Set-ADSyncScheduler -CustomizedSyncCycleInterval 00:05:00
The above command sets the sync period to 5 mins. It's important that you do not set the sync period too low, so that sync jobs don't begin to clash. A delta sync should not take a full 5 minutes unless the AD of a large enterprise scale.