Countdown Timer, front end input

I have no idea how this works if I would need a plugin made for me or if it's as simple as sticking one into my page but I need a countdown timer that anyone visiting my page can use.
There are plenty countdown timers but all that you set up in the back-end of the website. I need a countdown timer that I can add to my pages on my website that anyone can choose a time to countdown from there and then. Here's a few examples of what I am looking for:

https://www.tickcounter.com/timer
http://www.estopwatch.net/countdown.html
https://online-timer.en.downloadastro.com/tools/

Further information:
It is for my wordpress website - www.getyourhaircut.co.uk
When signing up barbers I realised they don't want bookings like salons, but a queue system which I could set up with private pages, mounted tablets in their barber shops and then creating a list for people to go in and add themselves to and the barber could set the timer without the need for changing pages.

Many Thanks,
Robbie