Adjust interval between tick marks in a graph

[fradhe]

It is impossible to adjust the interval between tick marks when displaying an horizontal axis with 2 categories (years and weeks). The following steps do not change the space between the tick marks.
• Select the graph;
• Chart Tools – Lay Out;
• Current selection – Horizontal (Category) Axis;
• Format selection;
• Axis options;
• Interval between tick marks: 4.
How can I change the interval for the tick marks to display a mark after every four weeks? Is this a bug or by design?

Thanks in advance.