Excluding dates in a appointment

[MacTI]

I'm trying to remove dates from a recurrence and I can't figure out how to do it. Let's say I want to create a sequence from January 12th to January 15th, but the sequence can't be done on January 14th. I tried the following :

<soap:Body>
<CreateAppointmentRequest xmlns="urn:zimbraMail">
<m l="10">
<su>Agent showing</su>
<inv>
<comp allDay="0" class="PUB" transp="O" fb="b" status="CONF" name="Agent showing">
<s d="20090112T150000" tz="(GMT-05.00) Eastern Time (US &amp; Canada)"/>
<e d="20090112T160000" tz="(GMT-05.00) Eastern Time (US &amp; Canada)"/>
<or a="mtmls134@zimbra.os.ca"/>
<alarm action="DISPLAY">
<trigger>
<rel neg="1" m="15" related="START"/>
</trigger>
</alarm>
<recur>
<add>
<rule freq="DAI">
<interval ival="1"/>
<until d="2009-01-15 15:00:00" tz="(GMT-05.00) Eastern Time (US &amp; Canada)"/>
</rule>
</add>
<exclude>
<dates>
<dtval>
<s d="20090114T150000" tz="(GMT-05.00) Eastern Time (US &amp; Canada)"/>
</dtval>
</dates>
</exclude>
</recur>
<fr>scdasdcdacdc</fr>
</comp>
</inv>
<mp ct="multipart/alternative">
<mp ct="text/plain">
<content>scdasdcdacdc</content>
</mp>
<mp ct="text/html">
<content>&lt;html>&lt;body>scdasdcdacdc&lt;/body>&lt;/html>
</content>
</mp>
</mp>
</m>
</CreateAppointmentRequest>
</soap:Body>

According to the soap-calendar.txt pseudo documentation, that should do the job, but it doesn't work. And I can't find a example because neither iCal, Outlook or ZCS Web client have a GUI to manage such an exception :-/

So, how can I skip days/hours in a sequence?