Every activity (quiz or presentation) has a particular join code that needs to be shared with participants so they can enter and attempt the activity. These codes are valid until the activity expires.
You can copy the code or the join link and send it to the participants of your activity. However, if you have invited them to join the activity via Groups, the join code will be sent to them automatically.
Join Codes for Live Activities
In a live activity, the join code will be active as long as you, as the host, are hosting the activity. That means the code will become inactive when you end the activity.
Join Codes for Assigned Games
The join code for an assigned activity will be active until the deadline for the activity arrives.
On the whole, join codes are valid until all participants finish attempting the activity or until the host ends the activity. If participants are yet to complete the activity, and if the host does not end the activity, the join code stays active for a few hours and eventually expires.