You will find an account-wide Activity Log under the Tools menu of the top navigation bar. This will bring you to all the general changes that have been made across the account. The events will be listed chronologically, with the most recent change listed at the top of the page. On the far left the time and day indicates when the change was made. In the same line on the right of the log you will find what type of change was was made to an Artist, Object, or Contact (Premium Only).