I agree with Rodabod. $360 should buy better accuracy than that. If they have any pride in their work, and want to keep receiving your business, they won't balk at taking it back in, nor at regulating it properly without charging you twice. The idea is to be so pleased with their service that you don't mind parting with the $360.
That's not good enough, assuming you measured on a full wind with the correct parameters. I'd take that back.
Be careful telling them that you used a timegrapher. Sometimes that causes the argument of "you think you know everything just because you are able to measure something". It may be easier to say that the timekeeping wasn't as good as expected and you had it measured by someone else.