httptest table contains a field nextcheck, which controls the next time of execution. If the delay of a check gets modified (API or WebUI), the nextcheck remains the same. Only after the next scheduled run the new value is calculated according to the recently adjusted interval.
Normally it is just fine and does not bother anyone. But troubles appear when the delay gets decreased significantly, e.g. from 3600 to 30 seconds. The new frequency starts working only after the whole hour of waiting.
I propose to change this behavior and set nextcheck to NOW()+delay on delay configuration changes