Good question. I shall preface my answer by saying I am not an expert, or a coach, or a scientist of any kind.
I have however, taken the HM many times and it really isn’t an overly taxing test (unlike its counterpart Full Frontal )
Honestly, I doubt it will make that much difference. If you want a clear sense of your progress to date, you could take the test before you go out of town. I don’t believe you’ll lose that much fitness over the span of 2 weeks. When you come back you could just pick up where you left off and see how the workouts go.
Or, you could hold off and do it when you come back so you will have the most accurate training targets based on that point in time (probably the smarter thing to do).
You could even do it twice. HM is not so overly taxing that it will completely wipe you out. Doing it twice can satisfy your desire (if you have one) to know how well you progressed as well as providing you with accurate metrics going forward.