I suggest, most likely but not yet certain that the breeding has failed, which would not seem odd, given that it is through mid winter. To expand on Geoffrey's comment there are various possibilities:
1 Eggs might be infertile and they are still incubating.
2 Eggs might be fertile but embryos have died and they are still incubating.
3 Might not be on eggs now.4 Maybe the start time you noticed is wrong as in they may have started sitting before eggs were laid (unless you know when eggs appeared).
5 Maybe the start time is now wrong if they had one clutch that failed e.g. through predation and they laid a second clutch, and you would not have known, so the start time needs to be reset. So the nest might still be successful.
6 Maybe chicks have hatched recently and they are still so small that you have not seen them yet.
Whilst I am on it, I will mention, having just noticed in checking this book for anything useful to add, that Betty Temple Watts also did the paintings for H.J. Frith's book Pigeons and Doves of Australia.
3 refs give 14-16 days for incubation. Eggs might be infertile or might not be on eggs now From: Dennis Ayliffe [ Sent: Wednesday, 1 August 2012 12:46 PM To: Canberra Birds
Subject: [canberrabirds] Bronzewings still sitting, sitting, sitting...
The bronzewing pigeons nesting in my garden have today entered their 4th week of sitting. My meagre resources don't give any figures for incubation time for the species. Does anybody out there have any information that might help me figure out