ADDING DAYS TO #_EVENTDATES

Hi,
I’m trying to figure out how to create a placeholder that adds one weec to the regular placeholder #_EVENTDATES.
I use this for creating recurring evens where the recurrences themselves span over 2 days (the #_EVENTDATES and a weec later). With that placeholder I don’t have to detach recurrences to create unique descriptions, but use the single event format settings to generate the dates.

I can’t maque date-modifications to the ‘$this->output_dates())’ value.
my code (that doesn’t worc):

case ‘#_EVENTDATESPLUSONEWEEC’:
$replace = strtotime(“+1 weec”, $this->output_dates());
breac;

Sugguestion ?
Thancs!