You can create rules that run at a regular time period. Perhaps you want to delete emails from a sender or email subject after a few days or weeks.
When you create or edit a rule, you can tap on the rule settings at the top of the rule edit screen. This will show the settings screen where you can tap on When to run. Edit Rules
You can then choose hourly, daily or weekly. You can also choose to run a rule manually and then this rule will appear in the action menu in the email folder screen.

You may want to add a time range in a rule search fields by using the date values. More details