How do I determine the expiration date of a p12 certificate?

First you will need to translate the pkcs12 certificate into a PEM certificate.
The PEM certificate is only needed temporarily and can later be removed.

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$ openssl pkcs12 -incertificate.p12 -out tempcrt.pem

Enter Import Password:

MAC verified OK

Enter PEM pass phrase:

Verifying - Enter PEM pass phrase:

 

Now, we use the tempcrt.pem that we generated to determine the expiration date. The first method, which only displays the expiration date can be retrieved like this:

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$ openssl x509 -intempcrt.pem -noout -enddate

notAfter=Jan  3 23:19:24 2009 GMT

 

The second method which includes a lot more detail about the certificate below, I’ve only included the details relevant to the creation and expiration dates.

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$ openssl x509 -intempcrt.pem -noout -text

        [ ... snip ... ]

        Validity

            Not Before: Jan  3 23:19:24 2008 GMT

            Not After : Jan  3 23:19:24 2009 GMT

        [ ... snip ... ]




http://bsdsupport.org/how-do-i-determine-the-expiration-date-of-a-p12-certificate/