Understanding the Calendar

[JVonD]

Trying to figure out how the calendar works and have been trouble shooting it a lot.
I'm under the impression that if you take a bunch of 30second jingles and then code like this,
<event type="playlist">
<playlist loopatend="1" shuffle="inherit" priority="1">
jingles
</playlist>
<calendar
repeat="255"
timeoffset="00:15:00"
duration="00:00:30"
/>
</event>
then the only way that the jingle will play is if the song on the original playlist ends within the duration time. So a song would have to end within 00:15:00 - 00:15:30 otherwise the jingle will be skipped..?
So if you have a bunch of longer tunes you're chances of every hearing a jingle is slim..?
Can anyone confirm that? Thanks ~J