Idea of Date Span Icon
There are two rectangles. In the bottom rectangle, there is a double-sided arrow. The arrow is in the center of the bottom rectangle. The top rectangle is connected to the bottom rectangle. There are two square on top of the top rectangle. They are to the center left and center right of the top rectangle.
This page shows the different variations of the Date Span from an Icons8 icon pack. Feel free to resize and recolor the icon, and then download the icon in PNG format for free.