Return the time elapsed since the last call to update (i.e: the last frame), in milliseconds.
Get the time since the instanciation of the manager (i.e: since the beginning of the scene most of the time), in milliseconds.
Get the time scale.
The time scale (positive, 1 is normal speed).
Return true if update was called only once (i.e: if the scene is rendering its first frame).
Set the time scale: time will be slower if time scale is < 1, faster if > 1.
The new time scale (must be positive).