You want to change your dyno's timezone.
To change your dynos timezone you have to add a
TZ environment variable to your application.
heroku config:add TZ="EST"
For daylight savings:
heroku config:add TZ="America/New_York"
Note: Changing your dynos timezone is not usually a good idea. Best practice would be to store/use time in UTC and instead convert the UTC time as appropriate at the view layer/client side for display only.
Note: this will not affect logs, as these are always in UTC.