In my experience, most strains of Brett in secondary show character at 3 months or so and are very nice by 6 months. Waiting for a year has never been necessary with the Brett beers I've made, though I have waited that long. Just bottled a strange Brett-Lacto beer at 16 months old and it's fantastic. But that waiting was necessary for the Lacto, not the Brett.
The Yeast Bay Saison-Brett blend often shows Brett character in as little as one month but, of course, gets stronger after that. I have a few beers sitting on that yeast now and some are showing minimal Brett at three months old and one is showing intense Brett at 4 months old.
Also, it is not necessary to take Brett C up to 85. If you're using it in primary, it's nice at an elevated temp like that but it's also nice at a cooler temp. A couple of years ago, I made a 100% Brett C beer (The White Labs strain) and pitched at 63. Early fermentation was 65-67, then warmed up to 71 for finish and aging. Left it at 71 for 3 months when I left town for an extended period. Checked it as soon as I got home and the Brett was entirely dominant and lovely. Have also used it at 85 or so and it's really great. Versatile strain of Brett, I'd say. Never used it in isolation for secondary, only along with other strains, so can't say exactly how it will behave on its own in secondary as far as Brett strains go. I wouldn't want to leave a beer aging for extended periods above 80F, though.
If I were you, I'd leave it around 70 or so for three months then take a sample and taste it. If you have no Brett at that time, wait another month or two and check again.
Everybody has different experiences with Brett and this is just my experience. Not saying anyone else is wrong but some of the information I see posted here is not what I have experienced with the 30 or so batches of Brett beer that I've made in the last few years. With Brett, though, patience really pays off. Just brew some more while you're waiting. I have 7 batches of Brett beer aging and at various ages right now. Makes it easier to wait when you have a bunch of them in the pipeline.