Hi Reba,
Welcome to the forum! Please see below for more information. The oath ceremony doesn't always take place at the time of the interview. It sounds like your husband should be okay. Lots of luck to you both!
http://www.uscis.gov/files/article/M-476.pdfBeing Interviewed
"¢ Receive an appointment for your interview.
"¢ Go to your local USCIS office at the specified time.
"¢ If requested by USCIS, bring identification and provide additional
documents. It is recommended that you also bring 2 additional passport-style
photographs to your interview.
"¢ Answer questions about your application and background.
"¢ Take the English and civics tests.
"¢ Receive a decision.
Taking the Oath
"¢ Receive a ceremony date.
"¢ Check in at the ceremony.
"¢ Return your Permanent Resident Card.
"¢ Answer questions about what you have done since your interview.
"¢ Take the Oath of Allegiance.
"¢ Receive your Certificate of Naturalization.