That is one of those question that falls under Every cat is different. Some respond very quickly, others take awhile. There is really no way of knowing until you start treating with insulin and testing them at home. I have two adopted diabetics, Maxwell with diet change alone and 2 weeks on a low dose of Lantus went into remission (off insulin) and has been there ever since (going on 9 months now). Musette I just adopted and she is still a work in progress. It really kinds of depends on how quickly they are diagnoised, and if there are underlying health problems, infections, bad teeth etc.
Some of the things you can do that will help Merlin along that path to good health, is change his diet to low carb/high protein and we have lots of options to do that and not break the bank.
Learn to test him at home, as most cats are under stress at the vet's and stress raises blood sugar. This also not only gives you truer numbers but keeps money in your wallet, and keeps him safe while on insulin....We can teach you how to do it
And ask your vet o start him on a nice gentle long lasting insulin..the 3 that are the best are Lantus, Levermir, and PZI.
I'm sure others will be along shortly with links to get you started. Normally I would, but Musette has decided to throw me a curve ball this morning (see I told you she is a work in progress.. :lol: )
But I did want to pop in and welcome you to the best place you never wanted to be, but are so blessed to have found.
Mel, Maxwell, Musette & The Fur Gang