How do I use a service property in a route?

I have a service that handles user authentication and gets the user data via a model. One of the pieces of data that it fetches is a date for the start of a dietary program. I want to use this date to calculate a number: the number of days since the start of the program, so I can use that number to query a different model that pulls content from a CMS.

I haven't been able to access that number anywhere other than a template.

This is the Controller for Dashboard

import Ember from 'ember';

export default Ember.Controller.extend({

  authManager: Ember.inject.service('session'),
    });

This is the template

  You are on a cleanse that starts 

  
  You are not on a cleanse.

All of the above code works, but when I try something like this in the controller:

  activeCleanse: Ember.computed( function(){
    return this.get('authManager.currentUser').then( (user) => {
    return user.cleanse_active;
    }.bind(this))
  }),

  startDate: Ember.computed( function(){
    return this.get('authManager.currentUser').then( (user) => {
    return user.cleanse_start;
    }.bind(this))
  })

And replace the template with:

  You are on a cleanse that starts 
  
  You are not on a cleanse.

It doesn't respond to activeCleanse being false (the template only seems to be checking for its existence) and the date tag only shows [object Object].

I am actually trying to get the date in the controller so I can manipulate it to pass as one of the parameters to the dashboard route, which gets a model based on the specific day:

The Dashboard Route

import Ember from 'ember';

export default Ember.Route.extend({

  model() {
    return this.get('store').queryRecord('cleanse-post', {
      filter: {
        tag: 'day-1'
        }
      });
    },

});

I want to be able to dynamically set the tag for the filter based on the calculation for the date.

Any help would be appreciated. I feel like I've been going in circles with this and I have no idea what to try.