The information below is official vacation policy of the university, which you should read. Please let me know of any extended travel you would like to take in advance. Generally, if you are taking the day off on a short-term basis, I don't need to be informed unless it conflicts with an existing obligation.
Graduate students and postdoctoral researchers are paid to pursue research as a full-time commitment (i.e. they are considered more as employees in this capacity). In other words, graduate students and postdoctoral researchers are expected to carry out their research activities during the summer and between semesters (i.e. during semester "breaks").
The vacation policy for graduate students and postdoctoral researchers is quite different than when one is an undergraduate student. Official university policies regarding vacation days can be found below. Note that the four weeks for graduate students includes any vacation days taken during regular University holidays and scheduled recesses.
The above information is not relevant for undergraduate researchers who are only expected to work in the group during the semester unless otherwise stated, as they are generally pursuing research for credit.