When having for example device set to US culture , the TimePicker shows 12h time format, which is correct. 

If you want to keep the US culture but want to use the 24h time format, the TimePicker does not apply the format, it still uses 12h time format.

The same behavior happens in the time part of the DateTimePicker

Allow for up/down arrows to step up/down the time element with the keyboard cursor. For example, if I have my keyboard cursor on the hours of a time, then pressing up would increase the hour by 1.

Keyboard support for the dropdown... Space to open, tab and/or arrows to cycle through and change the date/time.

The wheel stops nicely at first, but afterwards jumps into the next value, while I haven't released my finger from the wheel at any time. Still the wheel jumps from the initially highlighted and stopped value onwards to the next one.

So mainly, when stopping spinner scrolling, value is highlighted under the finger, when it should only stop the wheel.