What is the "duration" mentioned in the "Before you take the test" section for the certificate?

Is it that the certificate will expire after the “1 or 2 months” option that we’re getting?

No, the certificate will not expires in 1-2months
You can use your certificate when ever you want.it will be valid.
I hope you got clarity about certificate.
If you have any more doubdts you are free to ask.