[USG FLEX H] Allow DDNS Check Period lower than 5 minutes (e.g. 1 minute)

Zyxel_Judy

On USG FLEX H, the DDNS "Check Period" currently has a fixed minimum of 5 minutes. This means that in the worst case, after a WAN IP change, it can take up to 5 minutes before the device even notices and starts the DDNS update — which matters for anyone relying on DDNS for remote access, VPN, or similar services.

This was originally raised by @Maverick87 here: USG FLEX H – DDNS public IP, decrease minimum check period

Proposed idea:
Lower the minimum Check Period to 1 minute. Most DDNS providers cap their DNS record TTL around 60 seconds, so going below 1 minute is unlikely to bring much additional benefit on the DNS resolution side — but going from 5 minutes down to 1 minute would meaningfully cut the worst-case detection delay.

If you'd find this useful too, feel free to vote/comment below so we can gauge interest.