One easy way to hack this is by looking at your browser’s History right after you finish a study session. It will display the time that a page was visited. You can see the beginning of the “timer” when the first Codecademy page was visited, and if you see that a non-Codecademy page was visited, you now know when you tabbed away, and similarly, when you returned. Add it up, and you’ll get a rough idea of how much time you spent on Codecademy.
You may have to remember to manually refresh your page when you get back on Codecademy, or change some setting in your browser’s preferences so that the page automatically refreshes every time you tab back to an existing tab.
It’s probably best to do this as soon as you finish your session, so you can supplement the browser’s history data with your own memory, if needed.
Hope this was clear / helpful!