NEMO has usage reminders that users receive to remind them they are still logged on to tools.
You can also set up kiosk tablets to make it easier to start/stop using tools in the lab. If you are using area access tablets to badge in and out of areas, NEMO will also have a screen when they badge out that reminds them they are still logged on to tools and offer them a way to log off directly from the tablet.
Otherwise, you can charge them and they will eventually learn?
If you charge them, you can have them submit adjustment requests when they forget to logoff and when the adjustment is approved it will change the original usage times.
That's all I can think of of the top of my head.
Maybe someone else has a better option.