It took a little extra research to work out what was possible when, but I think I've got it worked out. After all, time is my playground, right? It still gets tricky when some science that wasn't tested until the 1980s is needed in the late 1960s, but sometimes some great plot convolutions come out of having to reconcile an anomaly.
My readers can look forward to a little more about the technicalities of time travel in this episode too. I've actually already written part of a conversation in chapter four that explains some temporal time/space Physics to explain why the characters can't keep going back and enjoying the same concerts over and over again. What a pity!
There may be a lot more of that sort of thing before I'm done. This new character gets around a lot. We may all learn a lot as a result.
Speaking of which, I found a great link for defining time travel terms. http://www.andersoninstitute.com/time-travel-terms-and-definitions.html