If you are cooking that hot, I'd guess between 2-3 hours. I did a boneless one a couple of weeks ago; I don't remember how big it was, but info about the cook is here:
Although the total time from cook start to meal was slightly more than 3 hours, at least 20 minutes of that was the turkey resting before I carved it. Looking back, I didn't cook it as hot as you are planning either.
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