two questions about time synchronization

[casso1993]

An offline embedded device collects lidar and IMU data, RTK timing IMU but no timing lidar. There are two cases:

1. If I use these two sets of timestamps directly, glim will give me a warning: [2025-07-07 07:15:05.662] [glim] [warning] large time difference between points and imu!! [2025-07-07 07:15:05.662] [glim] [warning] points=1483231948.200026 imu=1751872505.660600 diff=268640557.460574 But glim can build the map successfully , although the laser seems to have a little delay

2. When the driver receives the data, I try to use the system time to time the lidar and IMU, and send it in ROS data format. The warning disappears, but the mapping fails.

Question 1: Why is the map built successfully even though the timestamps are not aligned? Question 2: Why does the mapping fail when the time synchronization is successful (although there is a slight error)?

In addition, I tried to subtract 3E8 from the lidar timestamp after time synchronization. Case 2 becomes case 1, which is the same as above.