AWS Health Event/Scheduled Maintenance Window

When you receive a scheduled maintenance notification for your instances, you can perform a manual stop and start at a time that suits you, which will migrate your instance to new hardware. This manual stop and start can be done as soon as you receive the notification, and there is no specified minimum waiting period before the scheduled maintenance window. You can take this action immediately upon receiving the notification, or at any point before the scheduled maintenance date that is convenient for you. The key is that stopping and starting the instance yourself (which is different from rebooting) will move it to new hardware and effectively resolve the scheduled maintenance event. This gives you control over the timing rather than waiting for the scheduled maintenance window to occur.
Sources
Manage Amazon EC2 instances scheduled to stop or retire - Amazon Elastic Compute Cloud
Manage Amazon EC2 instances scheduled for maintenance - Amazon Elastic Compute Cloud
Scheduled events for Amazon EC2 instances - Amazon Elastic Compute Cloud