@LL0rd With the 7206 under Omada control, the router can be set to check the connection as ofthen as 1 second.  I don't know if you can have it check that often in standalone mode.  The way it checks the connection, is by sending a ping out the WAN interface, but I don't know if the timeout for dropped ping packet also goes down if you drop the interval down to 1 second.  Mine is set to 15 seconds, and I've seen it not catch dropouts of under 30 seconds, that windows will notice the dropout.

  @JoeSea Thank you for your Answer. My 7206 is also configured with Omada. And I also have this "Custom Time" setting set to 15s. But even with this setting, I get problems. First I don't think, that the router will drop the line, if I get a high latency ping back. But with a ping of about 1s, the Line is nearly unusable. You know, with Opnsense I can define what high latency is and when the router is going to consider the line as not usable. That's what I'm currently missing.