On your RingByName home page click on your name at the top right hand corner and choose the option "Go To System Administration". Click "Menu" on the left side of the page. Choose the name and click "edit". From there choose the "Options" and the "After Hours" tab and choose the person you wish to under the "Voicemail" tab.
To change the hours in the drop down box to match your work day, click the option "Hours" and set up the hours to match the times your business is in operation.