How to view email opens and their time of activity per recipient?
Generally, the date/time stamps on email opens by recipient can be retrieved via the results tab of a smart campaign. If the emails were sent via an email program, go into the Control Panel and click the View Results link in the Audience pane.
The other ways to get the activities and time by recepient is to:
1.) Create a smart list to find all leads that have opened the specified email and inspect each activity log
2.) Use the activities REST API