About 7-8 months. I was initially Dx'd with type 2 at 30 years old. My symptoms: the peeing, thirst, tired all the time, I'm very nearsighted so I don't recall vision problems, weight loss- got down to about 105 lbs (I am 5'6"). Using (I am presuming) only the age criteria I got the type 2 Dx. I was found by a neighbor in DKA coma - she noticed I didn't leave for my day job. Fortunately, my day job was with the city fire dept, they knew I had D and dispatched from the Chief's office. In the ERM the4 attending Endo got it right from the very start.
An additional hassle was in the ICU. They assumed that because I was 30 and it said type 1 on my chart, that I had not taken care of myself. So I got lectured during rounds several times a day. Finally my "hero Endo" asked - during rounds how long I had been Dx'd with type 1. I answered in a number that was a few days and hours. That shut the RNs and residents up.