I know it is a bit of a thread move but to be honest I do not think i have ever had an on time push back at LHR never mind an early one. I usually despair when getting an early puch back and taxi for early departure en route to LHR cos it ends up waiting for a stand at LHR for what seems like an age.
I do however smile when we get going early out of or inbound Bristol with EZY - then you can really can say early away and early in! And this has happened more often than not in my fairly recent experience.
Nivsy