I have always found it easier to synchronize AD Passwords with Office 365.  It’s a bit of work to set up initially but it works best for clients and it maintains the synchronization every 30 minutes or so.

There are times when it’s helpful to force a synchronization. 

Open PowerShell on the DC:

Start-ADSyncSyncCycle -PolicyType Delta

 To initiate a Full Sync, open Windows PowerShell and run:

Start-ADSyncSyncCycle -PolicyType Initial

If the commands are not visible, try to load up the PowerShell module:

Import-Module “C:\Program Files\Microsoft Azure AD Sync\Bin\ADSync\ADSync.psd1”

Usually synchronization happens within a couple of minutes depending on the size of your AD.