In the German version of the program, the "Timer" type of alarm is called "Stoppuhr", which translates specifically to a stop watch and not a countdown timer. I would recommend using "Countdown" in German.
Further notes:
I initially dismissed the applet and went looking for a different application, because I assumed it did not in fact have countdown timer functionality.
Unfortunately, there is no proper German translation for "Countdown Timer".
"Countdown" is basically used as a German word. It is so common that I have seen "Countdown-Zähler", "Zähler" being German for "Counter".
"Timer" is also used in German, but it is far less common and next to its actual meaning it is also used to market notebook format calendars/planners. (Probably because "Planner" is too close to German "Planer", so it doesn't sound "professional" enough. Marketing...) So there is some potential for confusion about the term.
Alternatives:
"Timer": Not recommended, possibly confusing
"Countdown Timer": No confusion, but might be too long for the button.
"Eieruhr" (lit.: "egg clock") or "Eierwecker" (lit.: "egg alarm"), if you really want a German German term. Both are terms for "egg timer".
In the German version of the program, the "Timer" type of alarm is called "Stoppuhr", which translates specifically to a stop watch and not a countdown timer. I would recommend using "Countdown" in German.
Further notes:
Alternatives: