Worry not. You dont need to justify your time, you only need to justify your thesis and what is written in it. Anything else wont exist for the duration of the defense exam. You are there to defend the data and results of your research, and any question outside of that you can redirect back to your thesis.
For example, if you have a research in pokemon evolution and you are asked about the time of the research, you says that the methods presented on your thesis, in Chapter 2, section 'XXXXXX' denote the process's own time, and therefore help validate the results, which are appropriately and consciously revised as can be seen in the conclusions chapter in section 'YYYYYY', which point to the prof/disproof of the original hypothesis.
Remember that you are defending your thesis, it's methods, and the results (and maybe, awfully too, the historical/theoretical frames). Unrelated questions are actually tricks from the examiners to derail you.