How do I configure a "Do Not Disturb" period? e.g. 1am to 5am

First, click on the Alerts navigation item at the top of the page.

Then, select Contacts.

From there, click on the icon in the Do Not Disturb column corresponding to the person / channel whom you want to create a DND period for.

Follow the instructions to create a new DND period. You can create as many DND periods as you like.