Should I alter personal holidays for a research visit?
How important is the research to you? And how hard is it for you to replan? 

An enthusiastic grad student probably would jump onto the opportunity, but if you see it as a chore, and you do not see direct repercussions (after all, they asked you whether it works), you might decline it.

Of course, you may still be enthusiastic, but it may mean losing out on a pre-booked, expensive trip to the outback/jungle/mountains/etc. (or something else that requires a lot of organisation and/or money to arrange). In this case, the decision will be less clear-cut.