not sure why that mod would display the timer in action tbh…
all I can say if my entity is updated per second, it shows without issue.
and on a button too
this is all that is needed for that:
- type: custom:button-card
entity: sensor.second_updater
show_state: true
and with notification:
- type: custom:button-card
template: styles_cf_notification
entity: sensor.second_updater
show_state: true
custom_fields:
notification: >
[[[ return entity.state; ]]]
if the issue would lie with displaying a timer (sorry I dont have one to test, but will do so later on), you could maybe go around that more easily (than modding all sorts of unnecessary stuff) by creating a template sensor on the attribute of the timer and add it to the button like I just did here
edit
confessing I cant make it happen either using my proposed techniques, sorry bout that. As it stands the attributes isnt even updated in the state machine and a regular jinja template cant make that happen either.
its probably in internal timer and I do have a script somewhere using that, but have to find that…
btw start reading here Display remaining seconds of timer in frontend - #46 by 123 where all of this has been discussed, sorry I hadnt looked that up earlier
this works though:
{{10*60 - (now() - states.timer.tester.last_changed).total_seconds()|round()}}
to give you an idea to work with, showing the time left in seconds, so you would only need to format that to your liking (and make it use the timer setting, instead of my hard coded way now)
btw tis works fine:
- type: custom:button-card
entity: timer.tester
show_state: true
out of the box 