@bplo, @kernelsandurz, @SteveC, @Skalman and others, I just found those two “automatic” commands working well (as tested) and useful with GNOME on Librem 5 (after Date & Time manually correctly adjusted and actually having connection to the Internet by having, for example, sudo apt update working with Wi-Fi/Ethernet):
sudo apt install ntpdate
sudo ntpdate-debian
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