According to issue with picamera2 [BUG] is it a bug. Truncate (right shift) ExposureTime with long exposures. ArduCam 64Mp HawkEye · Issue #1124 · raspberrypi/picamera2 · GitHub In my opinion there is a bug in libcamera software.
when I set time longer than 3.4 s time is right shifted to be shortet than 3.4 s.