setDateTimeFormat adds an hour

I would like to display my x axis in the hh:mm:ss format. It basicaly works, but there is one problem. The displayed time doesnt start from 00:00:00 but from 01:00:00. I thought maybe its because the time is in ap mode, but I havent specified that, here is how I do it:

customPlot->xAxis->setTickLabelType(QCPAxis::ltDateTime);
customPlot->xAxis->setDateTimeFormat("hh:mm:ss");

And the plot at point 0 starts from hour 1:

I would appreciate all help regarding this. How to make the starting point 0 shown as 00:00:00?