ktimer software package provides countdown timer, you can install in your Debian 8 (Jessie) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install ktimer
ktimer is installed in your system.
Make ensure the ktimer package were installed using the commands given below,
$ sudo dpkg-query -l | grep ktimer *
You will get with ktimer package name, version, architecture and description in a table
| Distro | Debian 8 jessie |
| Section | Utilities |
| Package | ktimer |
| Version | 4:4.14.2-1 |
| Description | countdown timer |
| Sub Section | utils |