Microsoft
A quick update.. the delay and random scheduling I was experiencing is apparently "by design", it is caused by Microsoft's global throttling policy.
Throttling configuration is randomly configured by Microsoft on a per-device basis. This essentially renders the phased deployment ring approach useless with the standard, well documented configuration. 
In the snippet below taken from the log files you can see the MROThroVal=5 and the MachineThroVal=177. This essentially means the update will not download until the MROThroVal is the same or greater than the MachineThroVal.. In my case this took five days 
According to Microsoft support the only way around this is to use the updatetargetversion value which will apparently override the throttling configuration.
So it appears all is not lost..
I will be testing this come patch Tuesday and will report back with another update (no pun intended) 
Richard
