Well, I just checked.
I stand corrected on my original post. I falsely remembered that they went to November 5, 1955.
However, the date was November 12, the day of the clock tower lightning strike. They simply went first thing in the morning. The DeLorean was in the lab so the spot behind the billboard was available.
However it is intereting to note that, at one point in the trilogy,. there are five versions of the DeLorean (maybe six) that exist all at one time.
I believe the time is 1955.
The one Marty used in the first Back to the Future.
The one the old Biff used to give the young Biff the almanac.
The one Marty used in the Second Back to the Future to fix the alternate timeline.
The one hidden by Doc in 1885 and fixed by them later.
Also, considering the law of Thermodynamics, the ray materials for the original DeLorean exist in some form some time in 1955, not assembled,