Thinking on this some more: if you want all the 1 o’clocks to line up, regardless of the date, then things are a bit more complicated… Date axes represent actual identifiable absolute instants in time like “1 o’clock on April 13th”, so all you can do in this case is normalize all times to a specific date e.g. Jan 1, 1970, which is the beginning of the unix epoch, and then force the date axis to show only times and not dates using tickformat.