Any activity detected after 00:01 will count as activity the next day. Therefore, if for example, there is activity detected from a toilet sensor or a landing motion sensor after midnight and you've configured this alert to let you know if there's been no activity by 9am, you will not receive a notification.
The "All Device" alert will notify you if there has been no activity from any sensor by the time specified in the alert rule. You will continue to receive an alert every hour thereafter if there continues to be no activity detected from any sensor.
Our alerts system is constantly evolving and we are currently working on the ability to exclude specific sensors from alerts. If you have any feedback or feature requests in relation to alerts, please do let us know by logging a ticket.