For automations like this, most people either use a second sensor outside the bathroom to establish a baseline for comparison or they use one of the statistical sensors to determine when the humidity is rising quickly.
There are a number of existing blueprints, like this one that you can use for you situation.
If you just want a sensor that tells you the value of your humidity sensor an hour ago, you can use a SQL sensor to retrieve that data from your existing database. The query would be as follows (make sure to use your own sensor entity id):
SELECT state from states
where entity_id = 'sensor.YOUR_SENSOR'
and last_updated_ts <= strftime('%s', 'now','-1 hours')
order by last_updated_ts DESC LIMIT 1;