This is a good point. There is a bit of a chicken-egg issue if the system time is set improperly such that you can't perform a secure TLS handshake. The issue w

This is a good point. There is a bit of a chicken-egg issue if the system time is set improperly such that you can't perform a secure TLS handshake. The issue we were concerned with is factory resets (say you resold the appliance or had issues) would accept old certificates. Malicious actors could use a brief window to exploit the system and perform permanent modifications that could withstand factory resets. IoT is especially scary, since often the first authority is a local Wi-Fi network. Users can easily be deceived to configure the wrong network, and become exploited. Additionally, users can easily exploit system clocks in many products to install custom firmware which, when resold or returned may then be passed on to other users. Does Amazon reflash all consumer electronics that are returned? Lastly, we decided to use a combination of HTTPS, certificate pinning, and client certificates to fetch a remote timestamp. We also use other, signed timestamps when available, but permanently record the most accurate time we suspect we have received. Devices cannot rewind prior to this, so if you have a device that has been offline for four or five years, you may be vulnerable, but chances are you are very vulnerable at that point anyways. If your device connects at least once a year, you should be good. Most devices connect constantly throughout the day.