Data from email service provider ReachMail show that open rates can vary dramatically throughout the day, and the data are different on weekdays and weekends. The peak time for opening appears to be mid-day on weekdays.
The take-away is that marketers should send their email in late morning, shortly before the peak, to ensure being at the top of the inbox.
Weekends are an overlooked opportunity for email marketers. Research shows Saturdays had a longer time-frame for email opens, or an extended peak, also around mid-day.-Tanya Irwin