How often are email reports created?

It usually depends on how many filters you have specified for the smart list (more take longer), but within 10-15 minutes you should start seeing some kind of activity.

Hmm, it's been 2+ hours since I've sent the email.

Have you tried logging out/back in? Were there a ton of filters on the list? How large was the list size?

This happens to me when the email didn't actually send. You should check the activity log of some of the contacts to see if there was an error. 

The email definitely sent as I see data in the "Results" tab, just not in the "Email" tab. I tried logging out and logging back in. I refreshed the report. I had 8 filters on the list and the list was ~5,000 leads.

Same problem happen to me, if you find any solution, pls let me know, thanks

It ended up populating the next day. Ever since then it's been working pretty quickly, within a few minutes of sending.