Bar widths in Report Builder (it’s quite similar in Visual Studio):
What you are looking for is in the properties grid under General–> Custom Attributes –> PointWidth
You have to select the series first.
If you can’t see the properties grid you need to enable it from the ribbon. View, check the box next to properties.
Numbers less than 1 will give gaps between the bars, number greater than 1 will cause the bars to overlap.
It’s more of a relative width setting than absolutely related to your particular interval, but you can tweak it so it looks right.
Personally I would suggest you have it slightly less than an interval because they look better with gaps.
You should also set the labels on the horizontal axis to be vertical and then rotate them so it looks a bit better.