Template sensor using time from attribute of another sensor

[clever rampart]

Hi, here's one of my sensor's attributes, i'd like to check, weather the last_time_reachable was more than 5 minutes ago.

I guess I need to use template sensor, strptime and compare that with 5 minutes. But I'm having trouble with proper strptime format to parse what I have.

{{as_timestamp(now()) - as_timestamp(strptime(state_attr('device_tracker.desktop_betrtn6', 'last_time_reachable'), "?????"))}}

here's a little work in progress formula

[random goblet]

Maybe try:
{{ (now() - state_attr('device_tracker.desktop_betrtn6', 'last_time_reachable')|as_datetime).seconds > 300 }}

[clever rampart]

will try