From what was mentioned up thread it's a glitch but it doesn't affect actual crafting times.... you just have a lot of time left when the timers finished...

Quote Originally Posted by Destiel0918 View Post
It happened to me once. Instead of reducing the timer by50%. It once doubled it. I was crafting wisp lanterns - 4 h timer. During boost- it showed 8 hours. After it was done.- it still had like 5 hours to craft - MORE than original FULL timer for this item.