What is the name for these vertical bands in this graph?
As shown, the chart elements could be referred to generically as intervals or time periods.
The duration of each of them is implied to be one twenty-four hour civil day beginning at midnight during a sequence of days.
The implication of the number is that some measured event achieved this (peak) value during the specific 15 October interval.
As there are also Month and Quatar [sic] buttons, the chart elements would have variable proportions and relative sizes to portray the data consistently with the overall term for the sequence selected.
That's a line graph laid over a column or bar chart.
Each vertical element is a bar, or column. When all the bars are the same height it's a timeline.
Each vertical section is a day so the columns are in calendar format.
You can call each vertical section a section, a node, a day, a bar, a column, a block, an element, a value, a data item or a chart element.