If you want to express locations on the globe in a mathematically useful and language and culture-independent way, you are best to use latitude and longitude rather than place names. That avoids all sorts of confusion and ambiguity. Where is this "Deutschland" you speak of? Oh, you mean Germany. When you say Boston do you mean the city in Britain or in the United States? Etc.
Similarly, for time periods the most mathematically useful and language and culture independent way would be to give a numerical date.
Of course a date is not entirely culturally independent. We have to agree on the lengths of the time units. Do we use years, months, and days? How do we deal with leap years? If we want a system that will work for people on other planets, Earth years are not very meaningful. Etc. What is the starting point of our calendar? The Gregorian calendar uses the birth of Christ (most historians agree it uses an incorrect date for this); the ancient Roman calendar used the date that the city of Rome was founded; etc. I'd say to use the date the universe was created as an objectively independent date that has the side benefit of avoiding negative numbers, but then you get into debates about just when that was. But presumably a time travelling civilization could agree on some standard calendar.
Of course people would probably still talk about "eras", because descriptive words are easier to remember than numbers. Historians routinely talk about the bronze age, the iron age, Middle Ages, Renaissance, Age of Exploration, Industrial Age, Space Age, Computer Age, etc. (Which suddenly reminds me of the middle-aged lady in the 1950s who, when she came to a place on a form that asked "Age", wrote "Atomic".) There's no definitive list of such eras. But a time travelling civilization might well make up a "standard list" of eras with specific start and end dates. If they have to deal with this all the time, it would be reasonable to make up such a list.
I don't time travelers would use past/present/future, as this is totally relative to the person speaking. It would be like asking where someone lives and he says "the north". North of what? With time travelers, if person A tells person B he's from "the future", does he mean person B's future? Future of the time they are in now? Future of some event they have just been discussing? Way too vague for identification.