IAM: How Best to Test Message Timing (on Session Start)

Hi Theresa,
In order to ensure that your audience is equally divided you can use a "Random Bucket #" filter.
For example, you can do this in the following manner:

• Bucket numbers 0 to 2499 correspond to the control segment
• Bucket numbers 2500 to 4999 correspond to the segment that will receive variant 1 (3rd session)
• Bucket numbers 5000 to 7499 correspond to the segment that will receive variant 2 (5th session)
• Bucket numbers 7500 to 9999 correspond to the segment that will receive variant 3 (10th session).

You can use it in campaigns with Target Audiences or with Canvas components such as a Decision Step or Audience Path.

As for the Xth session triggering, you can achieve this by a combination of the "Random Bucket"  and  "Session Count exactly 3/5/10" conditions on a Session Start triggered IAM campaigns.
Also, these campaigns could potentially trigger a follow-up canvas by interaction (view) with them if needed.