Subtracting from current time device class timestamp

Configuration
,
1

I am struggling writing a template and notification to know when a server watched with tailscale has been over 600 seconds since last seen.
I have ‘sensor.synback_last_seen’ that is device class time stamp
outputs like this
2024-03-19T01:43:46+00:00
what is the easiest way to write a template and also have a trigger for an automation

I put this below in my templates.yaml that outputs something like this for ‘SynBackUptime’
0:02:06

but not sure how to evaluate it to know if it is greater than x seconds

- sensor:
    - name: "SynBackUptime"
      unique_id: "SynBackUptime"
      state: >-
        {% set boot = as_timestamp(states('sensor.synback_last_seen'))|int %}
        {% set duration = as_timestamp(utcnow())|int - boot %}
        {{ timedelta(seconds=duration) }}
2 
- sensor:
    - name: "SynBackUptime"
      unique_id: "SynBackUptime"
      state: >-
        {% set boot = states('sensor.synback_last_seen')|as_datetime|as_local %}
        {{ (now() - boot).total_seconds() }}

The as_local may not be necessary depending on whether your sensor’s state contains timezone offset data.

3

works great, thanks!