I love to share infographics and this one I discovered from internet
The top engagement times for email are as follows:
in the mornings, 8 AM to 9 AM both for opens and click-throughs
in the afternoons, 3 PM to 8 PM for opens
3 PM and 4 PM for click-throughs.
This data was gathered from email marketing software who in turn analyzed 21 million messages sent from US accounts during the first quarter of 2012.
Review the graphic below for more details