Well first of all, I wouldnt call myself an expert by any stretch of the imagination, but heres my advice.
keep your diamond at 28 degrees 24/7 til it is about 12 months old. Then 4 hours a day of basking at 32/33 degrees from september til april, Then 2 hours of basking at 32/33 degrees from april til september with the odd day or two with no heat whatsoever. Do not feed during this time. Be sure you have a good thermal gradient, you pretty much want the cool end to be ambient room temperature.
I live in Geelong and my diamond has been cooling since april 14th, she hasnt eaten since then and is coping really well with the freezing southern temperatures. Last night it got down to 5.4 degrees in her enclosure. She just sits coiled up on her log conserving her body heat patiently waiting for her heat lamp to come on at 8am. Its really amazing how they cope in freezing conditions.
I got her out this morning and her tongue was in slow motion, as her body temp increases, her tongue gets faster and she gets a bit more active.
As you said, they DO need an annual cycle, just like they do in the wild or they WILL die in captivity.
I like to think of it like this. Imagine you were an eskimo and your family and all your ancestors have lived in the snow for generations and generations......Then someone comes along and locks you in a sauna at 30+ degrees for 24 hours a day??? Your body wouldnt cope and your organs would shut down, Thats what happens to diamonds if you cook them.
Hope this helps...
Cheers