Missing the obvious in this template.... checking fo a change to state more than 30 min ago

I need to check the state of an input_select since that last happened, compared to now, being longer than half an hour ago.

      condition: template
      value_template: >
        {{(now() -
           states.input_select.activity.last_changed).total_seconds()
          > 30*60 and
          is_state('input_select.activity','Opstaan')}}

makes it happen, but couldn’t I use another template that is much simpler? In fact Ive now split it up, while I suspect this can be done in 1 better template…

change to ‘Opstaan’ was more than half an hour ago…

please have a look? thanks!