Assuming firewall is required, the following 2 results were found.
the source link listed below but the settings didn't solve the problem. The solution was to change the options on the mac firewall by going into Settings > Security & Privacy > Firewall Click the lock to make changes Firewall Options Untick "Block all...
setting this to anything less than 4 hours worth, or your computer might get banned by the time servers. Change Your Firewall Settings Third party firewalls will often block the time servers, causing the sync to not work properly. If you are using...