first, you should be wary of mentioning using palladium material to replicate another Intellectual Property.. it can be real easy to slide into discussion of outright 'conversion', which will get the thread locked.
and Trans Dimensional Teenage Mutant Ninja Turtles is the book you want for time travel rules and building time machines. however, i will point out that by the rules in that book, you cannot put a time machine into a Sports car, which is the catagory the Delorean is in (the book actually provides stats for said type of vehicle) since you can fit them into smaller and larger vehicles, i suspect that restriction was done to avoid people being able to build a certain time traveling delorean in game. however if you want to allow time machines to be added to sports cars, as the Gm you can overrule the book. you just need to decide the cost of the modification.
as far as time travel rules work.. TDTMNT does not allow for you to go anywhere in time. you can't pick a specific year, day, or hour.
imagine the timeline as a spiral. you can't move along the spiral in either direction.. but you can jump the gap between the lines. so from a point in our time, you could jump to say, a few hundred years back, like the civil war. or to ancient greece. or to a few points in the time of the dinosaurs. and so on. you can go back or forward 50, 100, 1000, a million years, etc.. but you can't go back or forward anything less, or go to times between those points. not 51 or 49 years, for example. nor can you pick specific times you land. you'll basically arrive at the same hour, day, and month as the date you left, only the year will be different.
also, the flow of time is always forward. if you go back to the time of the dinosaurs, and spend 3 hours there, coming back to our time you'll find 3 hours have passed here. if you spend another 3 hours, then go back to the time of the dinosaurs again, you'll find that 6 hours will have passed since you left it. you can never return to the same time period before you left it.
you can still play around a bit with cause and effect, using things like letters left in storage or encountering particularly long lived people several times*, but you'll never have to worry about running into yourself in a previous adventure.
*actually, in some of the sample adventure/plothooks in the book, the characters encounter a certain NPC in several different time periods.. he just lives a long time, and each time period he is different as a result of how he lives so long.. depending on the order in which you meet him, you might encounter his "far future" self first and be met with vague comments about previous encounters that hadn't happened yet.
