What's the biggest time suck in your workday? If you answered email, research shows you're right. Professionals spend an average of 28 percent of every workday on email. That's two hours and 36 minutes.

We can collectively cut that time way down by adding one simple sentence to the end of every email we send. The sentence should say something like this: "If you can, I would appreciate a response by ____, so that ____." For example, to a potential customer: "If you can, I would appreciate a response by Wednesday afternoon, so that we can lock in the pricing we discussed." Or, if you're messaging an employee: "I need an answer to these questions by noon tomorrow so that we can meet our deadline on this project." The important thing is to let the recipient know when you need a response and why. Even better, if something isn't urgent, let them know that. "This is important but not time-sensitive, so please get to it whenever you have a chance."

These suggestions are based on comments from Wharton psychologist, TED speaker, and best-selling author Adam Grant, during a recent webinar for the online writing assistant Grammarly. In response to a question about workplace communication, Grant referenced research by Cornell's Vanessa Bohns showing a big mismatch between what senders expect from email recipients and what those recipients believe is expected. The reason is something called "egocentric bias," which leads most of us to think we understand what others are thinking and feeling better than we actually do. (For example, people usually believe they "get" sarcasm in emails when actually they're often wrong.)

In this case, our egocentric bias causes us to think the sender is impatiently waiting for an answer when that might not be true at all. "When you send an email, you don't usually expect an answer within an hour," Grant said. "But receiving that email? 'Oh, no! If I don't answer in the next four seconds, everyone will think that I'm a bad person and it will ruin my reputation and our relationship!'" Grant said that feeling was especially familiar to him in dealing with his own email.

But, he said, research also showed that the simple act of stating explicitly when you expect a response makes a huge difference: "Clarify expectations and say, 'I would love to hear back from you in the next 48 hours,' or 'This email is so low urgency that if you get back to me next month, we'll be fine.'" Being transparent about your expectations takes the pressure off recipients, he said. "As opposed to this sense that 'I have to fight a fire that just showed up in my inbox.'"

We check email an average of 15 times a day

The result is that the people you email can schedule and prioritize their time according to what's most important and most efficient for them. For example, according to time management company Zarvana, professionals check their email an average of 15 times a day. (Does that sound familiar to you? It does to me.) What if your employees and other contacts only needed to respond to email three or four times a day? Or even once or twice? How much productivity would they gain by, say, relegating email to just one hour at the end of their workday?

How much productivity would you gain? As an email recipient, you can make this insight work for you, too. When you get an email asking for information or for you to complete a task, unless you can satisfy the request in a minute or two, try sending back a simple boilerplate response: "Thanks for your email! I'm working to get this to you. Can you let me know how soon you need it?" Pretty soon, we might all get in the habit of adding a time frame for response to the end of our emails.

And, Grant says, this practice shouldn't be limited to email, especially when dealing with your employees. He suggests making a commitment such as this: "I commit to answering any message from the core team within 24 hours if you flag it as important. The rest of the time, we'll give each other a couple of days to respond." He adds, "Something like that can make a huge difference for people's well-being, as well as their sense of connection."

Next time you send an email asking a question or for a task to be performed, just add one sentence saying when you need an answer. And get in the habit of asking that same question when people email you. In time, we could all cut down on the number of times a day we answer email. We'd end up less overwhelmed and better able to structure our work in the way that suits us best.

There's a growing audience of Inc.com readers who receive a daily text from me with a self-care or motivational micro-challenge or tip. Often they text me back and we wind up in a conversation. (Want to learn more? Here's some information and a special invitation to an extended free trial.) Many are entrepreneurs or business leaders who often feel like they spend entire days drowning in communications and responding to seemingly urgent messages. If that describes you, too, how much time and mental energy could this simple step save you?