I gave the interval some thought, and while I might have to increase it in the future, I think 5 seconds is a good place to start. This is just a single innocuous ICMP echo packet, not port scanning. And a single user can only set up 10 pings, so it will require quite some manual effort to generate some noticeable traffic.

When I implement HTTP checks however, yes, the interval will have to be in the minutes.