How to create Always Encrypted Certificate for specific time period?
When this first came out I had a blog post on this, creating the certificate via Powershell: https://justdaveinfo.wordpress.com/2015/10/15/always-on-encrypted-generating-certificates-and-column-encryption-key-encrypted_value/

Checking the documentation for the Powershell cmdlet New-SelfSignedCertificate you should be able to use "-NotAfter (Get-Date).AddMonths(24)"

https://docs.microsoft.com/en-us/powershell/module/pkiclient/new-selfsignedcertificate?view=win10-ps