These limits may change without notice to protect Google's infrastructure. Limits per day are applied over a rolling 24-hour period rather than a set time of day.
https://support.google.com/a/answer/166852?hl=en
User locked out of their account? Google Apps administrators can check the Users section of your Google Apps Admin console to find details on which limits were reached and when access will be restored. In some cases, an administrator can reset the Gmail suspension.
The following sending limits apply:
Limit type Description Limit