As usual: it depends. Why does it need to validate a cert? How acceptable is it if you get it wrong? Depending on the answer, perhaps "have a more reliable clo

As usual: it depends. Why does it need to validate a cert? How acceptable is it if you get it wrong? Depending on the answer, perhaps "have a more reliable clock" is the right answer (plenty of embedded devices certainly have a decent idea of what time it is, and if it's already big enough to validate TLS). It seems reasonably probable that the NTP server stops being available for a reasonable amount of time before you have no idea what time it is anymore and can no longer validate certificates; so depending on the device, telemetry might be a good idea too. It doesn't sound like a reason to give up, though :)