Google's turned on a set of public network time protocol (NTP) servers.
You'll find the servers at time.google.com – which resolves to 188.8.131.52, a rather less pretty IP address than the 184.108.40.206 and 220.127.116.11 Google uses for its public domain-name system (DNS) servers.
There's also time2.google.com at 18.104.22.168, time3. at .8 and time4. at .12.