The SetAxisLabelsFormat method controls the first line of the time axis labels. The second line is referred to as the crossover date.
You can explicity set the format of the crossover date using the TimeAxisLabels.CrossoverLabelFormat property.
TimeAxisLabels xAxisLab = new TimeAxisLabels(xAxis);
xAxisLab.CrossoverLabelFormat = ChartObj.TIMEDATEFORMAT_DMY;
Eliminate the crossover data by setting the TimeAxis.DateCrossoverMode property to NO_DATECROSSOVER.
xAxisLab.DateCrossoverMode = ChartObj.NO_DATECROSSOVER;