Tell the Customer the Project Is Finished When It's Not
I laughed out loud when a developer claimed that he finished a project on time when I knew it was a completely false assertion. "Come on! You gave the client a box of half-finished bits and then spent eight weeks making it work!" He sheepishly admitted this was the case. I pointed out that the client knew it wasn't finished, just as the development team also knew it.
You may get away with throwing the project over the wall to the customer and running away. You can rest assured that you won't be called back. You've broken trust, and implied that the client is stupid enough to believe the lie of false completion.
You budgeted one week for implementation, and find yourself spending the next month in cleanup. The client knows that you're not fixing deployment issues; you're finishing the project! A side effect of this is that if we fool ourselves about project completion, we don't learn from our estimation and control mistakes.
Bottom line: Call it finished when it's finished. If you're over time, at least have the guts to admit it.