Jumbo Timer

Jumbo Timer is a nice application made by Johannes Wallroth. It is a direct descendant of the Sharp Timer made by the same person.
The software is simple enough, it is a timer for your computer. However, there are many nice things in this program. First of all, the digital timer's view can be configured, so it can have any color combination that you want, blending in with your desktop's appearance if it needs to. The size of the timer can also be changed: from a very small to the size of your screen. This is a definite plus for people who need bigger fonts to read.

The timer can be minimized and an icon will stay in the tray bar where you can maximize it or change the configuration settings.

You can have as many instances of this program at once as you wish, and each of them can do a different task. One can be set up to count down, another one to count up and there is also an alarm mode.
The downside of the program might be the license price $29 dollars, although monthly discounts are frequent.
If you need a precise and reliable timer, then this is definitely one of your choices.