TF get the time of last transform

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Hello! I want to check if the tf2_ros::Buffer received a valid transform from A to B in the last x seconds (to throw an error in case of time out). So something like buffer.canTransform(A, B, ros::Time(0)) with an additional argument for how far in the past the transform can be.

Is there a way to get the timestamp of the last available transform so that I can compare it to the current time? This sounds like a pretty common use case to me, but I could not find anything suitable.

Thanks a lot!