The information below is official policy of the university, which you should read (since it is always good to know the policies in place). That said, I have no interest in counting vacation days and trust that you will be making steady progress on your research. Please let me know if you are going away for an extended period so the group can plan accordingly. In terms of the winter period, most research activity at the university will return to business as usual by the middle of January (even though the start of the semester is in late January).
For the winter period, it is suggested to return by the start of Wintersession so that you can attend useful workshops held on campus.
University Policy
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:
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). Standard university holidays and vacation policies apply, and the academic calendar is less pertinent. In other words, graduate students and postdoctoral researchers are expected to carry out their research activities during the summer and between semesters, excluding university holidays and vacation days taken by the researcher.
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.