No downtime. And even if there was, that shouldn't matter, since it's non PROD.
How do you expect us to do an impact analysis for you? We don't know your instance.
If you don't have the certificates automatically renewed, you will have to do it manually. But you can do it before the current certificate expires so there won't be any issue. Just put the new one in and the system will just take the new one.
If you use Google, you get lots of docs related to this. Here are a few:
https://support.servicenow.com/kb?id=kb_article_view&sysparm_article=KB0780908
https://docs.servicenow.com/bundle/vancouver-security-management/page/product/secops-integration-sir...
https://support.servicenow.com/kb?id=kb_article_view&sysparm_article=KB0691439
https://www.youtube.com/watch?v=A7tJuTi-dxA
Please mark any helpful or correct solutions as such. That helps others find their solutions.
Mark
