BTW, if you don't wanna use any DNS server, you should use IP addresses instead of names above. Above method might work better with DNSSEC, DNSSEC over HTTP and DNS over TLS, aka using unbound service. Not sure how those would impact my curl calls, not to mention the move to HTTPS!
And DD-WRT sets initial system time using a daemon called process_monitor, with hard-coded default NTP server IP address "184.108.40.206" (which is pool.ntp.org) when Basic Setup->Time Settings->Server IP/Name is blank!
as I responded to you hard code in the other thread:
poor form and actually could be a flaw to fall back to a default hard coded address. Everyone could have the error (or not even know) and then DDOS that one IP address or even what happens when that IP address has to go down for maintenance or is compromised? Oh and what if you are on IPv6 only or not connected to the regular internet but an isolated network?
ntp provides other options and slews the clock for a continuous time, and not having discontinuous jumps. If your clock drifted future in time and then you jumped backwards according to this method, now all of the logs are confusing and not making sense, not to mention time stamps and other things.
This algorithm also has no measurement of the time it took to get the packet and the time, so it could be a minute old or 47 seconds, or 0.5 milliseconds, that is unknown.