How long is overtime?

In Overwatch, if the attacking team is touching a payload or control point when the round timer runs out, the game will enter Overtime.

How long does Overtime last after the attacking team stops touching the objective?

Right now, my answer is going to seem like speculation, because it truly is.

Unfortunately, I cannot find any patch notes or dev announcements from Blizzard that specify exactly what the Overtime length is.

The subreddit, and many posts on the official forums (which 404 for me now, so I won't provide any links) seem to agree that it is ~10 seconds, and I can concur with that number from personal experience.

Example link from the subreddit expressing this belief: https://www.reddit.com/r/Overwatch/comments/3p0esi/there_doesnt_seem_to_be_much_info_on_the/