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
https://docs.marketo.com/display/public/DOCS/Locate+the+Activity+Log+for+a+Person
https://docs.marketo.com/display/public/DOCS/Filter+Activity+Types+in+the+Activity+Log+of+a+Person
OR
2.) Use the activities REST API
http://developers.marketo.com/rest-api/lead-database/activities/
http://developers.marketo.com/blog/get-activity-data-via-the-rest-api/
http://developers.marketo.com/blog/retrieve-activities-for-a-single-lead-using-rest-api/
http://developers.marketo.com/blog/polling-for-activities-using-rest-api/