Countdown template for 'last seen' of z2m device time

Hello!

Guys I have this templates sensor:

{{ state_attr('switch.entryway_wired_switch_right','last_seen') }} = 2021-09-11T19:03:57+03:00 is current attribute value of this switch.

My sensor:

          {% set last_seen = (as_timestamp(now())| round(0) - as_timestamp(state_attr('switch.entryway_wired_switch_right','last_seen')) | round(0)) | int %}    
          {% if last_seen == 0 %}right now
          {% elif last_seen < 60 %}{{last_seen}} ago
          {% elif last_seen >= 60 %}{{last_seen}} ago
          {% elif last_seen >= 3600 %}{{last_seen}} ago
          {% else %}unknown
          {% endif %}

And my sensor is back 59403 minutes ago value, what’s wrong? Can someone could explain this, what’s wrong in template? In the end I need x seconds, x minutes or x hours. Thanks.

Try pasting this into Developer Tools —> Template-

{% set t = (as_timestamp(now()) - as_timestamp(state_attr('switch.entryway_wired_switch_right','last_seen'))) | timestamp_custom('%H:%M:%S') %}
{{ t }}

back: 20:18:35