I was trying to do the same with AMF but haven't had much luck yet with the login process.
I'm using Charles Web Proxy which has a built display for AMF which shows the request to https://<vsm>/messagebroker/amfsecure with a 'destination' of VsmConfigFacade which returns the data. The AMF data is displayed in an XML tree style format in Charles so the field we want is under VsmConfigFacade.getVcConfig - /Results/body/vcInventoryLastUpdateTime.
The Value is a number in milliseconds that needs adding to 1/1/1970 00:00. So 1362658800715 becomes 07/03/2013 12:20 (English Data Format)
I'm working in Powershell v3 and just found this which may be useful: http://velemental.com/2012/01/31/powershell-and-adobe-amf3/
With a sample script for vmware view here: http://velemental.com/2012/02/04/unofficial-advanced-vmware-view-powershell-cmdlets/
Chris