Why not combine the two. What if you could write a time you spent on the feature directly into the commit message? Some VCS support this already.
It's a plugin which is not easy to configure but you can enter the time spent in brackets like this "(1h)".
Freckle Time Tracking (http://mir.aculo.us/2009/10/12/instant-time-tracking-from-git-commit-messages/)
"So Freckle Time Tracking now comes with Github integration, which means you can instantly log time from Git commit messages when you push updates to Github."
Entering times looks like this "f:2.5". More details: https://help.letsfreckle.com/import-export-api/log-time-from-commit-messages
Supports it since 5 years ago. Format "time 30 m" on a new line.
That's the largest issue tracker, of course it supports it. Format: "#time 1w 2d 4h 30m".
I'm the developer of a small time-tracking system and I don't use any of the above. So I've made a small PHP script which would analyze the commit log and collect the times from it. Format: "[0.5h]" or "[22:15-23:00]". The results would look like this, but it's easy to customize.