=Andy_R: Time for this one to go (a month later than planned).
For those interested, the theme was Back to the Future (part I).
To complete the solution:
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There and back again
This was a play on the theme of Back to the Future; Marty travelling to the past and back. Potentially makes one think of The Hobbit, which was a little bit of misdirection on my part.
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Dummy Coordinates Thousandths
Put together gave 030785 => 03/07/85 the release date of Back to the Future (part I). The hint Use the first pointed to the first film of the trilogy, and also to the first four journeys of the DeLorean.
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Toblerone Patent
Allegedly Albert Einstein signed the patent for Toblerone. Whilst it was true that he worked as a patents clerk in the office where Toblerone was registered and at the right time, it is unlikely that he actually signed the patent. (This is my favourite piece of specious trivia, and the inspiration for this cache). Einstein was the name of Doc Brown's dog, and the first passenger in the DeLorean time machine.
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Wonderland (2005)
An album by the band McFly, who were of course named after Marty McFly. Marty was the inadvertent second passenger in the DeLorean travelling back to 1955.
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Charles Monroe
Better known as Charles M. Schultz, the creator of Charlie Brown which should have led you to Dr Emmett Brown, inventor of the time machine, and the third passenger in the DeLorean. Admittedly this clue probably only made sense once you had already made the connection with one or two of the other clues.
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John Zachary
John Zachary DeLorean was the founder of the DeLorean Motor Company who made the DMC-12, the car that was converted to a time machine by Doc Brown.
So the 4 travellers were Einstein, Marty McFly, Dr Emmett Brown, and the DeLorean itself.
The four journeys were:
Time/Date Departed Time/Date Arrived
Einstein 26/10/1985 01:20 26/10/1985 01:21
Marty 1 26/10/1985 01:35 05/11/1955 06:15
2 12/11/1955 22:04 26/10/1985 01:24
Doc Brown 26/10/1985 22:04 26/10/2015 ??:??
So A= 1985, B=1955, C=1985, D=2015, taking the order in which the journeys occurred in the film, not the convoluted timelines. I was originally going to use the times and dates of the trips in the final decode but sadly this approach fell down with Doc Brown's trip to the future, as his exact departure time is unknown, as is his arrival date.