thx to this comment, i created now a fluid-app for me with eggtimer.com! there is always a time when u need one (and ur too lazy to ask siri to do it ;) )

but now i would love to have a option on fluid, that ask me for parameter when it starts, so i can set the timeframe when i start the "app"

Yes, its the same principle, but tested for years. They also have a non-flash ("mobile") version: e.ggtimer.com/m/5minutes