The most common way to make a timer is to use unixtime which is built into Construct 3. Unixtime is in milliseconds so you will need to break it down to seconds (/1000).
You will want to set your Timer to unixtime + the amount of time you countdown will be.
Then just show the text with the difference - Every tick (You can change this to every second or 0.5 seconds if you need to save on performance. But I have never bumped into an issue with every tick on all my timers)
Note of Caution:
Unixtime is loaded from the users computer. This means they can go in and edit their time and it will change the games unixtime.
Check back in about 11 hours:
I plan on making a video on this tonight after work. I will walk developers through creating a timer and displaying the timer in different way for their users.