you can't get rid of the delay , but there is a parameter accessable via maxscript to reduce the delay before the first progressive render iteration gets blended in ( introduced with Max 2013). This includes the AO if it's enabled
You can set it for the current viewport by usign the followign command in the listener ( default value is 32 btw )
(nitrousgraphicsmanager.getactiveviewportsetting()).ProgressiveFadingFactor=0
This should speed things up a bit, but don't expect miracles
Josef WienerroitherSoftware Developer & 3d Artist Hybrid