There's a website called Tiii.me that calculates how much time you've spent watching TV ... by having you enter shows that you've watched, and the number of seasons you've seen.
It's kind of fun to play with ... but at the same time, it probably isn't the best measure of the TOTAL time you've WASTED watching TV. Think about it ...
If you endured multiple seasons of something ... and it's a show that comes to mind off the top of your head ... it's probably something you ENJOYED.
As opposed to the hundreds of hours you've BLOWN watching mindless, repeated cycles of SportsCenter or HGTV ... without even really realizing it.
For example, if you've seen every episode of "Friends" once, that's 3 days, 14 hours, and 32 minutes. Then you can do it with other shows, and it adds them all up.