To view the expiry dates of an SSL certificate simply run
openssl x509 -noout -in <filename> -dates
Which will output data in a format similar to this
notBefore=Jan 1 00:00:00 2011 GMT notAfter=Jan 1 23:59:59 2012 GMT
If you wish to view all data stored in the certificate file you can run this which will show more details (and also includes the expiry date).
openssl x509 -noout -in <filename> -text