I have a diabetic cat. He's 15, and was diagnosed 3 years ago.
I am very conscientious about giving him his shots on time, and I think that helps keep him stable.
I gave up on the special diet, because I have 5 cats, and it's impossible to keep them separate (and I don't want to stick him in another room to eat). I just found a food that works well for everyone.
what do you mean "how long did it go on"? It doesn't resolve itself, if that's what you mean, except in some rare cases. It's going to "go on" for the rest of his life.
The shots are hard at first, but we're both very used to it (I'm also a pro at giving sub-Q fluids with a MUCH LARGER needle to one of my cats with kidney problems).
One complication he had at first was diabetic neuropathy, which causes the feet and legs to be weak. He got to the point where he couldn't jump up on the couch anymore, could use the stairs to go to the basement, and was walking on his back '' knees" (whereas cats normally walk on their 'toes"). The vet said once they get it, it's irreversible, but I did some internet investigation, and found that Methylcobalamin (a form of B12) has been used to reverse it somewhat, it cats AND people. I started giving it to Scooter, and about a month later (it takes time), he was up off his knees and able to jump on the couch again.