Microsoft Time
Most of us have long had a chuckle over the "estimated time to completion" or even progress bars which shoot to 99% and then hang there for ages. Basically the operation (file copy, install, delete .. whatever) is happening, but the guestimating of the remaining time has been thrown way out.
Here is what I would do, if I was a programmer of the dialogue box. Put a conditional on the time which checked to see if it was more than, say, 48 hours. In this case, simply report 48 hours "+" or "or more". Leave it as that, it's already a lot longer than anyone will really wait, and It's already highly doubtful that it's accurate anyway at that, so just give up. At least the ridicule would stop.
Biting the hand that feeds IT
