Just wait, be patient. You want lots of roots, not just a few.
It is pretty common for air layers to take more than 16 months to fully root. I have had air layers take as long as 3 years to succeed. Patience. Just keep it moist, and plan on checking in August, best time to separate is as the heat of summer ends. So when you no longer expect many more 95 F or warmer days, when night time temperatures start falling, in my area this happens middle of August, but I don't know when it cools off by you. That would be the time to separate the air layer. Sept or October would probably be the right time.