Question about the timestamp of Lidar pointcloud

[yangam16]

Thanks for your work. I have a question about the timestamp of pointcloud.
The frequency of lidar is 10hz, while camera 25hz. It's easy to understand that we should use timestamp to realize time synchronization. However, I wonder how to set the timestamp of pointcloud? Did you use the timestamp of first lidar point or the timestamp of the last one? There is a difference about 100ms between the two points.
Beg your reply.