I have released a small library that keeps the Particle Time sync’ed to an ntp server. You can use any server you’d like but it defaults to “time.nist.gov”.
It is simple and light. Just create the NtpTIme object and call the start() member function. Then forget it. It uses one of the software timers to keep the Particle Time well sync’ed.
Buyer bewares: It is not subtle about adjusting the time. If there has been a big offset, it could yank the time by quite a bit and mess up something depending on it. It tries to adjust the time to the tick of the second, but that might vary depending on your ntp round trip latency and the accuracy of the software timer.
Available on github at https://github.com/ClassTech/NtpTime/ , it is under the MIT copyright, so feel free to use it. Let me know if you have problems or questions.