When does the link "Acknowledge this service problem" hide?

[TerminalCondition]

Nagios Core 3.5.1

We have some services whose value for check_period and notification_period are "business hours" (8:00 am - 5:00 pm). Some services might be in a WARNING or CRITICAL state at 5:00 pm. I've explained to our support that, for example, this doesn't mean "My service" is in a WARNING state at the current time. It always means that "My service" was in a WARNING state at the "Last check" time.

Support would like to acknowledge warnings like these. I'm not sure that's a good idea, since the warning doesn't necessarily reflect reality. In any case, it looks like Nagios hides the link to "Acknowledge this service problem" if the current time is outside the check_period. It's not visible in the morning either; "My service" is always OK by then (so far).

Is the behavior I just described actually what Nagios is doing--hiding and displaying the link to "Acknowledge this service problem" based on check_period (or some other *_period)?

Is this behavior documented? If so, where?

[TerminalCondition]

Is the behavior I just described actually what Nagios is doing--hiding and displaying the link to "Acknowledge this service problem" based on check_period (or some other *_period)?

I found another service that was in a warning state, and it was outside its check_period. The link to "Acknowledge this service problem" was present.

So it looks like there's either a bug in Nagios (possible), or a misconfiguration on my part (more likely).