My last Berliner kept chugging for months (ma in October, kegged and consumed at a Cinco de Mayo party this past spring.... If you want it quick, then you should do a sour mash, then boil or approach 180f for short time then chill and pitch the yeast at ambient temps; or skip the Brett and go with the straight lacto pitch followed by the yeast a few days in. At least that is what I read from experienced sour guys around here.