Hi
Agree on the university vac terms, in terms of parking, overall city traffic, ability for students to attend... just the best option.
From managing a holiday house for a while, the December - April timeslot is by far the most popular for international visitors - I think that's when they are particularly gatvol of their Northern winters.
This obviously does not fit well with the usual time, but, and I don't know if Debian peeps have families, December seem to be a good time to tag them along.
So my preference for timings would be:
1. Somewhere around December, determined by the vac clots
2. April vac.
B