<p>There are two different types of flags that one can raise:</p>

<ol>
<li><p><strong>Moderator-only flags</strong> which can only be seen and handled by moderators.</p>

<p>These age-away/expire based on guidelines given in the following question:</p>

<ul>
<li><a href="http://meta.stackexchange.com/questions/204327/when-are-moderator-flags-automatically-dismissed-as-aged-away-by-the-system">When are moderator flags automatically dismissed as &quot;aged away&quot; by the system?</a></li>
</ul></li>
<li><p><strong>Review flags</strong> which go to their respective review-queues (low quality, close/duplicate).</p>

<p>Only canonical migration flags expire. Since, Ask Ubuntu doesn't have any canonical migration target (as of now), it is irrelevant for us.</p>

<ul>
<li><a href="http://meta.stackexchange.com/questions/207179/do-flags-to-close-expire-like-votes-to-close">Do flags to close expire like votes to close?</a></li>
</ul></li>
</ol>

<p>Based on my experience, most of the flags get handled within a couple of hours. However, in case of Review flags it can stretch to a couple of weeks. And, in case of Moderator-only flags which might require some investigation it can stretch to a couple of days.</p>

<p>As to your belief that since the flag is taking time to be handled, you might have raised a bad flag &mdash; don't worry about it. If a flag is taking time to be handled, it <em>generally</em> indicates that you have raised a good flag. I would leave its interpretation upto you :-)</p>