Always go early if you are in doubt about over-runs.
You really aren't losing anything, especially if your machine is doing less than 100hr/year.
We often end up with "60/80" hourlies(40 hours early), because a job cannot be completed within the available MR times.
It is illegal to operate on an expired MR, as stated before. Your insurance company will put it perspective for you, should something untowards happen.