In Scrum When Is a Sprint over?

The short and simple answer is that a sprint is over when the sprint timebox ends! ... (There is nothing in Scrum that says you can only release one product increment each sprint!). A sprint is also not over when the Sprint Goal has been achieved.

When should a sprint end?

Sprint Ends once the Sprint time-box expires. Ideally all the sprint ceremonies should have been completed.

How long should sprints be Scrum?

It's a rule of Scrum that a Sprint should never be longer than one month. Generally speaking, the Sprint length should be approximately three times as long as it takes to Swarm on an average medium-size Story and get it Done.