Does anyone have a succinct explanation about the physical laws governing time in Doctor Who? As events unfold in the series (I guess I'm mainly talking about the post-2005 incarnations) the Doctor and his companion move around at will in the mundane human 4D universe, but seem to be following some linear 'timeline' that threads their lives, as if there was an extra time-like dimension that the Doctor exists in that operates in the same way as 'our' time does for us, namely that it can only be moved along in one direction.
For example, 'The Time War' with the Daleks occurred in the Doctor's past. When he meets other time travellers, for instance Jack Harkness, they both believed that the Daleks 'had been destroyed', which implies a finality that goes beyond their ability to move around in our 4D universe at will. The same applies to Harkness's past.
Are there some canonical rules or explanation about how time operates in Doctor Who, or is it always mysterious and disjoint to the viewer?