/tf sends messages at different timestamp

edit

I have a /tf message that seems to send messages at different timestamps. I added comments "// Look here" to highlight the stamps in secs and Im mostly intrigued by the one with the comment "// Look here !!" as the time stamp in secs has absolutely different timestamp. However, the next after that one follows the the pattern as the majority.

Why does this happen?

--
transforms: 
- 
header: 
  seq: 0
  stamp: 
    secs: 1305031234        // Look here
    nsecs: 763107844
  frame_id: /kinect
child_frame_id: /openni_camera
transform: 
  translation: 
    x: -0.0112272525515
    y: 0.0502554918469
    z: -0.0574041954071
  rotation: 
    x: 0.129908557896
    y: -0.141388223098
    z: 0.681948549539
    w: 0.705747343414
- 
header: 
  seq: 0
  stamp: 
    secs: 1305031234           // Look here
    nsecs: 763107844
  frame_id: /world
child_frame_id: /kinect
transform: 
  translation: 
    x: 1.28183615112
    y: 0.60716934967
    z: 1.60902340698
  rotation: 
    x: -0.226407331155
    y: -0.209261051914
    z: 0.662704621347
    w: 0.682474993971
 ---
 transforms: 
- 
  header: 
    seq: 0
    stamp: 
    secs: 1551776935     // Look here   !!!
    nsecs: 528851222
  frame_id: world
  child_frame_id: camera_pose
transform: 
  translation: 
    x: 0.0543486074629
    y: -0.0490532501685
    z: -0.083467717153
  rotation: 
    x: 0.0249910632545
    y: -0.369232593093
    z: 0.0535471565154
    w: 0.927456436165
---
transforms: 
- 
header: 
  seq: 0
  stamp: 
    secs: 1305031234                 // Look here
    nsecs: 773104542
  frame_id: /kinect
child_frame_id: /openni_camera
transform: 
  translation: 
    x: -0.0112272525515
    y: 0.0502554918469
    z: -0.0574041954071
  rotation: 
    x: 0.129908557896
    y: -0.141388223098
    z: 0.681948549539
    w: 0.705747343414