Changed your code a bit.
Added this lines so it works now:
$startDateRow = $meta['wpvt_start_date'][0];
list ($monthStart, $dayStart, $yearStart) = split('[-.-]', $startDateRow);
$endDateRow = $meta['wpvt_end_date'][0];
list ($monthEnd, $dayEnd, $yearEnd) = split('[-.-]', $endDateRow);
$this->startDate = $yearStart.",".$monthStart.",".$dayStart;
$this->endDate= $yearEnd.",".$monthEnd.",".$dayEnd;
Usecase.
1 Add new timeline post
2 i click in the date field
3 calender pops up i choose
4 that the time is placed in the field like 03-26-2015
5 this one is not working {“startDate”:”03-25-2015″,”endDate”:”03-27-2015″,
6 this one is working “startDate”:”2015,03,25″,”endDate”:”2015,03,27″
its seems to be the date format, mine is 01-01-2015 thats not working, this one ist 2015,1,1 can you fix or can i fix that somehow?