If I’d only had a dollar for every time I heard that. Or, maybe an app that I could set to say “OK, time’s up”.
This was a computer science problem that I gave my students. It was one that easily scaffolded to a number of things like accessing the internal clock of the computer or writing code to do an eight segment digital display.
Here are a couple of answers that can help you with than dilemma if you’re not ready to spend the time to code your own.
Suppose someone just wanted 5 seconds of your time …
Online Stopwatch does a great job. 
It’s as simple as setting the time and clicking Start. In the classroom, if you have your computer connected to a data projector and time is of the essence, go to full screen and away you go. There’s a ringer at the end of the countdown so you may not want to test this out in the middle of the night when your wife is asleep. Just saying.
Look at the URL and you can edit it for any time that you want. Or, there are some preset times at the bottom of the screen. Or, back off to the root of the site and use the buttons to set things from there. Links at the bottom will take you to a bunch of other displays.
If you’re caught without your bookmarks and you can’t remember the URL, use your old friend Google.
Just search for – “set timer to 5 seconds”
What can be simpler!
I’m sure that you can find all kinds of ways to incorporate a timer into your time management routine. I’m thinking of those groupwork times when you’re circulating and engaging with students. It will help you with time awareness.
doug -- off the record 
Please share your thoughts here. I’d enjoy reading them.