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Using a time of zero works in python. It's in the tf python listener tutorial

There's a known issue with the epydoc based documentation in noetic. However since this package is deprecated there's been no API changes since melodic and you can use that documentation. It's actually barely changed for years before that too. You can just use the melodic documentation that you already linked to.

However it's not necessarily going to solve your problem because it still needs a "common" time. Aka for all links in the chain it need information at a "common" time aka the same time. tf does interpolation between different samples in time.

The simple solution is that you need to make sure that you have data in your listener from before and after the requested timestamp for all links in the chain. If you use TIme(0) you only have to make sure that you have any timepoint that's consistent and it will return the latest.

And although you don't want to move to tf2 in tf2 we added static transform support which does exactly what you want letting you not worry about time for a link because a static transform is considered to be valid for all times. So if that's what you want, you may actually want to look at moving forward to tf2.

PS As a side note your question makes a lot more assertions than asking for help and a lot of those assertions are inaccurate which means that you end up digging further afield. You may find that being a little more thorough in each step of your investigation may help you get what you want faster.