Hmm, what? I'm... not sure I really understand why you would need to get too clever with tenses, if I'm understanding you correctly.

I mean, the only real example of this sort of thing I can think of off the top of my head is Doctor Who, which has a few lines every once in a while where the use of tenses sound a little weird. For example, when the Doctor's in 1963 and says, "the Daleks already took over Earth in the 22nd century". Sure it sounds a little funny because he's using the past tense to refer to something that happens in the (objective) future, but you still know what he means, especially since it's implied he saw it happen in his own personal past.

So... yeah, tenses are weird in time travel stories, but I don't think it matters much since you can still pretty much understand the intended meaning behind things even if the correct tense to use in a given sentence is rather debatable.