Arun Sirpal pushes the big red button:
We all would like to save money when operating in the cloud, Microsoft has released a stop / start concept for SQL Managed Instances – preview mode!
At the time of writing, the Managed Instance needs to be built from the November wave where you will see the functionality in the overview section and it has to be in the General purpose tier. If you have managed links or failover groups then you cant use this feature.
There is a kicker, however, which makes this a less-than-pleasant option. Arun has more detail.