Check for external DragDrop

Is there a reason why in DragAndDropContainer we need to wait 700ms for check a external Drag?
if (canDoExternalDrag)
{
auto now = Time::getCurrentTime();

if (getCurrentlyOver() != nullptr)
    lastTimeOverTarget = now;
else if (now > lastTimeOverTarget + RelativeTime::milliseconds (700))
    checkForExternalDrag (details, screenPos);

}

Because the user could be … very slowly … moving the mouse all this time, and waiting 700ms is a ‘reasonable’ amount of time to wait to determine if the user has stopped dragging …