Under the chart properties, in the axes tab, you can set the scale's static step to 7 and the static min to "Min([Start Date])". However, this method will only work if there are no outliers. Once more dates keep getting added to the chart, QlikView will dynamically adjust the scale so that it can show the labels without any clutter.
An alternative solution to show the week start metric for the bar chart is to enable either the "Text on Axis" or "Text as Pop-up" display option in the Expressions tab (in chart properties). Hope that helps!