replacement for rospy.Time(0) in ROS2?

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Hi, I want to lookup the latest transformation in a tf buffer. In ROS 1 used rospy.Time(0), but I haven't found anything about how it works in ROS2.

Here is a snippet of the code to understand in the context:

tf_buffer = tf2_ros.Buffer()
tf_listener = tf2_ros.TransformListener(tf_buffer)

dur = Duration()
dur.sec = 10
dur.nsec = 0

transform_odom_base_link = tf_buffer.lookup_transform(target_frame='base_link',
                                        source_frame='odom',
                                        time=UNKNOWN
                                        timeout=dur)