One of the great benefits of the “online everything” world in which we now live is the ability to evaluate nearly anything about marketing not with hunches or speculation, but with hard data.

A perennial question is what time of day is best to deploy marketing e-mails to customers and prospects. The higher the propensity to open and read these messages, you’re closer to the goal of converting eyeballs to clickthroughs … and to sales.

ReachMail, a Chicago-based e-mail service provider, recently studied a large sampling (~650,000) of the millions of consumer and business marketing e-mail messages it sends out for clients daily in order to determine open rate differences based on the time of day. It normalized the data to account for different time zones.

What ReachMail found was that there are differing peak open rate times on weekends versus on weekdays:

 Weekdays: Peak e-mail open rates are between ~11:30 am and ~2:00 pm.

 Weekends: E-mail open rates begin trending upward at ~11:30 am, but don’t peak until ~4:00 pm.

John Murphy, ReachMail’s president, had this to say about people’s weekday e-mail open rate behaviors: “You would think it would spike in the morning, but they’re looking at work e-mails in the morning. Once they’ve cleared out their inbox, they’re looking at marketing e-mails in the afternoon.”

ReachMail’s conclusion: It’s best to deploy weekday e-mails between 10:00 am and Noon. For weekend e-mails, deploy them between Noon and 3:00 pm.

And this additional tidbit also: Don’t assume e-mails sent during the week will perform better than those deployed over the weekend. “People’s engagement rates are up there on the weekend,” Murphy maintains. “It’s our habit of checking e-mail all the time.”

He’s sure right about that.