Configure NTP Client - Installation - openHAB Community
Block your IoT devices from the internet but allow Time Synchronization ( Fritzbox) Block IoT devices from the internet but allow NTP Time Synchronization (Fritzbox)
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HowTo: ESPEasy - Activate NTP time retrieval from the Internet - Nerdiy.de - Nerdy DIY HowTo's about electronic, 3D-printing and more.