Thanks Mirek,
but it's a "problem" of accessibility. If I fix the number of the lines of the Droplist, then I've got the scrollbar and that's too thin to be used from a touchscreen. I should be able to widen that scrollbar too.
But I've thinked about that hour&min selection and I've choosen for two handmade EditIntSpin (a big label between two big buttons, a "+" and a "-"), because I can't enlarge the buttons of the "standard" EditIntSpin (and my solution is more accessible).