You sync to the NIST time servers (sample code available via linked page) via a cron job that invokes the script, whenever the IoT device is rebooted.

1. NIST Time Server Page: https://www.nist.gov/pml/time-and-frequency-division/service...

2. Crontab @reboot function: https://superuser.com/questions/708149/how-to-use-reboot-in-...

Make sure to always cite your references by comments. This is useful in case parts of your code become unintentionally obsolete. This also helps you and others proofread your work.

Depends on the device type, location and needs.

As for what most use to connect, WiFi, Cellular service and Satellite technologies are common. In my experience satellite is reserved for burst or alert type data given the low bandwidth and costs when it comes to IoT devices.

Depending on the device, it is not different from a computer when it comes to cloud syncing.

There are Linux distros focused on IoT devices, so imagine a compact version of Linux connecting to a cloud service.