People are really bad judges of little time. And they often don't signal their intentions appropriately. My friend Alexandra Wolfe pointed this out to me recently when she noted that people always say that they are running "5 minutes late" or that they will "be there in 5 minutes."
But what does "5 minutes" actually mean?
My investigation into this mystery has led me to the following answer: "5 minutes" means anything and nothing.
When you tell someone you will be there in "five minutes," it conveys no information. It could mean you'll actually show up in 1 minute or mean you will be there in 25 minutes. The person who gets the message won't know if they should eagerly await you or do a sales call.
And, by the way, it is the same thing for "20 minutes." no information is conveyed. "20 minutes" could actually mean "never."
So instead of saying you'll be five minutes late … tell people that you will be there at 5:06p. That gives a definite time to the receiver and will ease her anxiety. Plus, you'll be able to better signal your intentions so that they can follow you.
Also — never say you'll do something "in a sec." that's likely untrue. It is possible you'll do it in 16 seconds … but likely you'll do it some time longer in the future.