Extrapolation exception error (tiny time difference)

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Hi, I'm attempting to help some colleagues extract data from a rosbag. I'm running Ubuntu 18.04.5 LTS. A Hokuyo UTM30LX lidar was used to gather a pointcloud, published on the topic /slam_cloud with the message type sensor_msgs/Pointcloud. They would now like to extract the pointcloud data in xyz format or similar format. As the message type is Pointcloud and not Pointcloud2, I cannot use the pcl_ros bag_to_pcd node as I had hoped to.

Instead, I wrote a short script to subscribe to the pointcloud topic, and write each point to an xyz file. The pointcloud topic is published in the /laser_frame, so I would like to transform the data to the /map frame instead. However, when I attempt to use the tf.TransformListener.transformPointCloud() function, I get the following message:

ExtrapolationException: Lookup would require extrapolation into the future.  Requested time 1617028327.692719936 but the latest data is at time 1617028327.642892361, when looking up transform from frame [laser_frame] to frame [map]

The difference between the two times is very small, approximately 0.025 seconds. The topic is published at a rate of 40Hz (every 0.025 seconds) , so to me this seems that somehow the frames are 1 cycle out of sync. Strangely, if I run tf.TransformListener.lookupTransform('/map', '/laser_frame', rospy.Time(0)), then do not get an error message. I'm not quite sure where to proceed from here: as I can get the transform from lookupTransform I could transform between the two that way but I don't if there's a tf function I can insert the trans and rot arrays into.

Thanks for your help

My code is pasted below:

import rospy
import tf
import numpy
from sensor_msgs.msg import PointCloud
import time


class pointcloudlistener():
    def __init__(self):
        rospy.init_node('cloudgrabber')
        self.listener=tf.TransformListener()
        self.listener.waitForTransform('/map', '/laser_frame', rospy.Time(0), rospy.Duration(4.0))        
        pclistener=rospy.Subscriber('/slam_cloud', PointCloud, self.cloudcallback, queue_size=1)
        self.pointlist=[]
        time.sleep(3)
        while len(rospy.get_published_topics())>2:
            time.sleep(1)



        f=open("pointcloudfile.xyz", "w")
        for i in self.pointlist:
            message=str(i.x)+str(" ")+ str(i.y)+ str(" ")+ str(i.z)+str("\n")
            f.writelines(message)
        f.close()        

    def cloudcallback(self,pointcloud):
        trans, rot= self.listener.lookupTransform('/map', '/laser_frame', rospy.Time(0))
        transformedcloud=self.listener.transformPointCloud('/map', pointcloud)

        for i in transformedcloud.points:
            self.pointlist.append(i)

pointcloudlistener()