[zokier]

You don't need to trust the dhcp time. But it would be useful for bootstrapping, especially devices without rtc. This does not really apply to your average PC which probably already has good guess on current time, those can simply just ignore the dhcp provided value.

The DHCP server provided value can not be much worse than 1970-01-01T00:00:00Z default value if you don't have any other data. And if you have some other data, e.g. ext4 superblock timestamps, you can pretty trivially protect against DHCP providing time from the past (i.e. use the maximum of different sources).

Finally, you can restrict the use of the dhcp provided time to the initial bootstrapping process only; it's not necessary to use it for system-wide clock