If you create the certificate without specifying the days parameter, the default value will be taken, which is 30 days. https://www.openssl.org/docs/manmaster/apps/req.html
when the -x509 option is being used this specifies the number of days to certify the certificate for. The default is 30 days.
To cahnge this, specify the number of days you want your certificate to be valid. For a validity of 1000 days:
openssl req -x509 -new -key smp_sso2.pem -out smp_sso2.cer -days 1000
Resulting certificate:
Valid from 6.10.2015 to 2.7 2018
