QAbstractSlider and its subclasses (QSlider, QScrollBar) provide no means to change the default repeat delay (threshold) and interval (time), except from implementing your own event handlers. Other widgets that know repeat behaviour have such possibilities, either defined by the current style (QAbstractSpinBox) or directly per API (QAbstractButton). I suggest to provide setters and getters for this properties in a unified way, preferrably in the style of QAbstractButton, as this is most convenient to use.
Rationale: Manipulating the repeat timing and keeping it consistent throughout an application can be of importance e. g. for embedded UIs (increase usability with touchscreens and lagging display updates) and perhaps for accessibility (people with reduced reaction time).