If I start watching Back to the Future II at 4:25:39 PM today, the time circuits in the movie and the actual time will line up exactly when they first arrive in 2015.

They appear in the future 4 minutes and 21 seconds into the movie. The time circuits read October 21st, 2015 4:29 PM.

*Edit - The time circuits are obviously tuned to Pacific Time since it's the middle of the afternoon when they land in Hill Valley.

In the 1980s, when Doc Brown was programming the time circuits, daylight savings time ended on the last Sunday in October (this changed in 2007, but wouldn't matter either way since today is before the last Sunday).

So it is likely that the time circuits were displaying PDT, meaning the actual time I need to start watching the movie is 7:25:39 PM, Eastern Daylight Time.