The time elapsed between starting and finishing a project is only one element. The other is how active you were during that time.
I can spend months on end doing nothing at all for Essentials, and when I do work on it, it can either be a quick bug report-inspired tweak taking 15 seconds, or I could spend 4 hours on something - both would take up one day of my timeline, but the latter is obviously more effort spent (which may roughly equate to productivity). So yeah, activity level is another aspect people should be talking about.
I would say that another aspect is how often you found yourself doing work you ultimately rejected, but actually, I don't think you could just subtract that time and end up with "how long I took to make my game". Even if a particular feature or graphic or song you worked on ended up being rejected, you still gained experience and knowledge doing so, which undoubtedly had an effect on other things. Your game wouldn't be the same if you hadn't done the stuff that isn't in it.