This is a different solution, and less manual - but OralB has a bluetooth enabled toothbrush that will auto-record your tooth brushing in their app (as well as metrics like 'time used too much pressure' and 'total brush time'). You need to manually record flossing and tongue brushing via the app though (using a button on your smartphone like others have described). It's not bad, it's not good, but it's a start.