How to reduce the displayed Majorgridlines in order to match them to the "Category" texts?

Question

Within this picture, an Excel chart is displaying approximately 100 values + times (red curve):

Excel is "intelligent enough" to reduce the number of the displayed "Category" date+time texts (here: by the factor 6) because otherwise the texts would overlap each other. But the Excel chart still displays ALL the vertical (dark gray) grid lines where my value table contains time markers.

IF my data table contains even more (e.g. 1000) time values, then the displayed "Category" date+time texts are automatically reduced e.g. by the factor 60. But then the chart background is completely covered by vertical grid lines and does not show its background color any more at all.

In fact I would like to keep/show only those vertical grid lines where a Category (time) text is shown, i.e. ONLY at my green lines.

So how to to reduce the number of the displayed vertical grid lines ?

Thanks a lot