Yes,If alert is not addressed ,alert would re-trigger
Duration depends upon the alert if it's system generated alert(depends upon value or interval at which it triggers or event driven )
Thanks Shridar - in the link it states that it will re-trigger if scanned again, so I guess the thing to do if one is genuinely unsure if an issue was properly resolved is run a new NCC check.
Damn I accidentally hit best answer on my reply, sorry Shridar. This portal doesn't offer me a way to fix it. I sent a note to the moderator about it so they can fix it.