If using a NTP server to maintain the gateway 2 time, verify if the NTP server is configured as a name or IP address. If as a name (e.g. "pool.ntp.org", by default), you must make sure a DNS server is configured in the Gateway 2 network settings. If this is an IP address, you will not necessarily need a DNS server configured.
A list of publicly available time servers is available at http://tf.nist.gov/tf-cgi/servers.cgi - you are able to see both their names and IP Addresses.