<p>How long should it take to run </p>

<pre><code>ALTER DATABASE [MySite] SET READ_COMMITTED_SNAPSHOT ON
</code></pre>

<p>I just ran it and it's taken 10 minutes.</p>

<p>How can I check if it is applied?</p>

You can check the status of the READ_COMMITTED_SNAPSHOT setting using the
```
sys.databases
```
view.  Check the value of the
```
is_read_committed_snapshot_on
```
column.  Already
asked and answered
.
As for the duration, Books Online states that there can't be any other connections to the database when this takes place, but it doesn't require single-user mode.  So you may be blocked by other active connections.  Run
```
sp_who
```
(or
```
sp_who2
```
) to see what else is connected to that database.