How long do meta descriptions take to go live on Google?

I’ve done SEO for a bit but I’ve never had this type of client issue before. They want to rework all of their meta descriptions because the business owner hates what populates now. Nothing is setup in Yoast and screaming frog is pulling in no meta descriptions.

I want to set the right expectations with client. Has anyone monitored how long it takes for meta descriptions to go live in SERPs?