For the past few years I worked with "Open Dental" They have a fantastic feature that allows you to slide along a scale indicating timelines of when treatment was planned/ completed. It was a very helpful tool often referred to by Dentists in particular.
Simply drag your cursor across the scale and as you move it along it visibly reflects the changing treatment and timelines in the chart/ odontogram.
(You simply drag the cursor the same way you adjust your volume on a computer)
Below I have attached a snapshot off the Opendental website as an example.