For those who are interested in keeping track of how much time you are spending on a particular game, I use a freeware program called Manic Time
that's easy to use and keeps track of everything you do on your computer. It provides a detailed breakdown of time spent on every application, document, etc.
When I compare my times as recorded in Steam as opposed to the actual times recorded by the time tracker I find that Steam is not accurate but not that far off either. Steam says my time spent on my 2nd playthrough of DKS is 120 hours, actually it's 117 hours. In both cases that includes time AFK.