(1) Because Back to the Future is the story of Marty McFly, it consistently follows him around, not the DeLorean. Therefore, the several instances where he is not one of the time travellers (Doc in the future, Biff, Doc in the past) are not well-documented. This chart is the best I can do.
(1a) Example: When Doc travels to the future at the end of Part I / immediately prior to Part II, it is not clear exactly where (when) he went. His intended destination at the end of Part I was "30 years", so it is presumed by many (including me) that he traveled exactly 30 years forward, from early morning, Saturday 26 October 1985 to early morning, Monday 26 October 2015. He then learned the recent history of the McFly family: the future scenes in Part II take place on Wednesday 21 October 2015, less than a week prior. He may have made several jumps around in 2015 (or later!) but what is known is this: (a) he got a hover-conversion for the car, got the Mr. Fusion installed, went to a "rejuvenation clinic", and acquired (presumably, as opposed to invented in the past or present) the other devices he uses in Part II - the "neuralizer", a camera/scope device, snazzy 2015 clothes for himself and Marty, etc.; (b) he did some recon, gathering newspapers, and noted the precise location of Marty McFly, Jr. on 26 October so that he could be intercepted (Doc says "precisely on schedule" when he sees him); (c) he somehow filled a briefcase(!) full of money from different historic eras, at least including Civil War and World War I time periods; this past money would be difficult (or expensive!) to come by today (or in 1985); it would be far easier to acquire with (reckless) time travel; (d) at some point, he traveled to a few days (or weeks) before 21 October, when he dropped off Einstein in the suspended-animation kennel. (This jump I have shown.) So, he made at least one jump within 2015, but possibly many more, and he may have gone much farther into the future.
(1b) Example: When Old (2015) Biff stole the time machine, all we know is that he travelled to Saturday 12 November 1955 to give himself the machine. (I always speculated that he saw that date in some history log of time jumps made, although it wouldn't have been the immediate "where you last were" date. However, then Doc could have just checked the log himself later to see when Biff went. We probably have to go with Doc's speculation that it was either a "junction point for the entire space-time continuum," or else just "an amazing coincidence.") Biff could have traveled to many different times in history, and - as he is not shown using the machine in 1955 to either arrive or depart - he may have arrived earlier and/or stayed later than this date. However, I have assumed in my chart that he spent a small amount of time, maybe an hour, in the past.
(2) I have left off the very ending (as well as, naturally, the canonically questionable animated series and video game.) Thus, I show Einstein remaining in 1985, and Doc in 1885. Why? Because the ending just raises more questions than it answers
! (Warning: TV Tropes!)
(2a) How (and why!) did Doc invent a flying, time-travelling train? There are several problems with this. OK, obviously it took him 10 years or so, and he's built a time machine before so it shouldn't be as hard the second time. And if he really wants to, he can dig up the DeLorean buried in the mine in order to reverse-engineer the flying parts, etc., and then re-bury it later, but that really runs the risk of creating a paradox. He must have somehow made a time machine (without even rudimentary electronics existing), then traveled to the future (21st century) to get parts to make the train fly. But why would he even bother, if his last orders were to destroy the time machine? If all he cared about was giving Marty the picture, then he could have buried it, or written another letter or something. Anything else destroys his whole mantra that time travel causes more problems than it solves. And how practical would a gigantic flying train really be for a time machine, anyway?
(2b) His other stated reason for visiting the future. Doc says, "After all, I had to come back for Einstein." But... Einstein is already right there in the train as he says this. So... he came forward in time for Einstein, then went back to the past and then back again to 1985 to see Marty?
So, I left this ending off.
EDIT: According to TV Tropes, the date 12 Nov 1955 was given (in a deleted scene) to old Biff by his mechanic friend who (somehow) remembered the exact date of the infamous manure incident. OK, I guess that makes sense...
(3) For those who haven't seen the documentaries/deleted scenes/directors' commentaries, old Biff fades away shortly after returning to 2015, due to having been killed by his wife Lorraine in the 1990's; thus he was erased (dramatic pause) from existence. Anyway, I showed his (temporary) death as upon his return to 2015.