The times created by timechart represent the start of the period / span so aligning to the axis marker makes sense i.e. the anchor for the label is to the left and the data at this point in the chart is no earlier than the value of the label. There is no anchor point in the middle of the bar in the barchart with which to align the text even if you wanted to. You might be able to hack around this by formatting the time (strftime) with leading spaces, however, you may find that the chart viz will strip leading/trailing spaces before displaying the x-axis label anyway.