Hi Lacey,
Without knowing the actual date of your Advance Dining Reservation, I am unable to check what time dinner at
Hollywood & Vine starts on the day that you will be dining there.
If however, you go to the Hollywood & Vine page on the Walt Disney World website and select the date of your visit from the calendar icon situated underneath the blue box where it says "Book your Trip", it will tell you the times that dinner is served on that particular day.
(I have just checked the calendar for November 2, 2016 and can tell you that dinner will be served from 3:00 PM - 6:30 PM on this particular day.)
If your Advance Dining Reservation falls during lunch, you will only be able to see the Disney characters present at lunch. There is generally a period of around 75 minutes between the time of the last lunch reservation available to book and the first dinner reservation available to book.
Disney Junior pals including friends from Doc McStuffins, Sofia the First, Jake and the Never Land Pirates and Handy Manny are available for meet and greet during breakfast and lunch whilst Minnie, Mickey, Donald, Daisy and Goofy are available for meet and greet during dinner as part of Minnie's Seasonal Dining.
If you are in any doubt at all, I would recommend that you call (407) 939-1947 and have a Cast Member confirm which Disney characters will be in attendance during your 3:55 PM Advance Dining Reservation.
Wishing you a magical trip filled with memories which will last a lifetime!
Emma