- TLS - TLS mode will extract the current time out of TLS (i.e. SSL) handshakes. If you block NTP to WAN and don't run your own NTP server(s) internally, this is the only option. If you MITM SSL connections, your proxy will typically return random dates, which prevents this from working, so you must use NTP. This mode ignores the time servers set here.
- NTP - NTP mode will use NTP (really SNTP) to synchronise with the configured time servers. If you block NTP to WAN and instead run your own NTP server(s) internally, you must set them here. If you don't block NTP to WAN, you can leave these blank to use default public servers instead.