How to adjust cook time for heritage turkey

This year I decided to do a little extra and reserved a 20-22lb heritage Bronze from a local farm.

Every year I do the Williams Sonoma Buttermilk Brined Turkeyand it's incredible, my guests even fight over turkey bones to take home to make stocks ever year.

I want to do the same brine, but I'm not sure about timing and temps for a heritage bird. I'll be sure to butter between the breast and skin to hold in moisture and I think the buttermilk will help.

The usual time I do is in at 400 for 30 mins, then 325 for 4-5 hours. I'm hearing that heritage birds need a higher temp and shorter cook; should I shoot for 400 at 15 mins and 350 for 3 hours (get it to between 155-160f?)