Daylight savings time vs Epoch timestamp / template

In order to push time to my thermostats, I need to send: (Epoch timestamp I believe)

I’ve been using the following template but the recent DST change isn’t reflected
(time is 1h behind)

        - service: mqtt.publish
            topic: zigbee2mqtt/{{ device }}/set
            payload: >-
              {"thermostat_time": "{{ (as_timestamp(utcnow()) -
              as_timestamp('2000-01-01')) | int(0)  }}"}

both utcnow and now show the correct timestamp so not sure why this doesn’t work

I’ve tried adding | timestamp_local and a few other tricks but no success yet.

Let me know if you can help, thx!