How can Listen to Index refresh?

I will write a Plugin that scan a directory in periode. The Periode to scan are in the settings of the Index ("index.refresh_interval":"1h").
My Problem is, how can Listen the Index? It means a Service or Method must call every 1 hour. It give it a Listerer for it?

Your plugin will be in Java, so you can use any Java timers you see fit.
When you instantiate the plugin, you will get the settings, so you can
instantiate a timer at that point.



How can read the Index Settings in the Plugin ? Can I do this with the BaseRestHandler ?