I edge glue two recycled 1x4s to make medium boxes. I made a sliding jig for my tablesaw that the cut-to-length 1x4 rides on when squaring up the side edges of the board. By riding on the jig while cutting, there is virtually no opportunity for the board to move with respect to the blade (other than the direction of cut), and is more precise in that respect than using a fence. The sliding jig also means there is no fence resetting involved - or the
possibility 
that the fence may get set wrong.
If you plan ahead, you can make the same jig suitable for squaring up both edges of that board - just make a shim/spacer that you can place between the jig reference edge and the newly trimmed board edge prior to making the second cut.
FWIW, I am using rabbet joints with those edge glued 1x4s, but do ALL the gluing in one operation by assembling all the boards around a gluing jig that allows clamping in all directions at the same time. The lengths of the boards are cut such that the rabbet joints of the upper rank of boards alternate positions of the lower rank. As the edge joints and rabbet joints at the corners are all glued at the same time, The box is quite sturdy. Once the glue and clamps are applied, the joints get stapled. I leave the glued and stapled box alone for an hour or two and do something else while the glue dries. I have not tried unclamping immediately after setting the staples - I usually have something else to do anyway.