Hi @robotAstray thanks for this PR.
The tests (which required some activation) show one lint error that is easy to fix (move an import statement).
In addition, please consider the following points:
The usage of math.isclose(), which seems to be incorrect according to the function's syntax.
The change will not achieve the same thing as the current code, which returns the index of the entry with time equal to t in the array by exact comparison. This should be improved to return the index the entry in the array with time closest to t.
It is also best not to set a default value for t because all values would be equally valid and there's no preferred one.
If you are interested, please submit the fixes.
Thanks again.

@haggaila, thank you for the message, I will work on this and update you. Thank you.

@haggaila I made changes to the logic, I welcome feedback, suggestions. Thank you.
(I will add a docstring to the function shortly)

Thanks @robotAstray it looks better. I still see an issue - find_index_nearest_time_within_tolerance() may return None which will crash the invoking code. I'd say that the index of the closest entry should be returned, and in any case we would need to test the function to verify that it works as expected. Thanks.

Hi @haggaila, I've made some changes to the code based on your feedback. I've addressed the issue regarding the function returning None and added proper handling to ensure that the index of the closest entry is always returned. Additionally, I've added comprehensive tests to cover different scenarios and ensure the correct behaviour of find_index_nearest_time_within_tolerance(). The trailing newline issue has also been fixed in test/plot/__init__.py. Please let me know if there's anything else that needs attention. Thank you!
(I also think test_plot_routines.py may be used to add tests for other functions belonging to plot_routines.py I can work on it in another PR if needed)