Somewhere like 6 to 7 probably, but remember to allow for resting also so you have a fairly large smoking window there. I always plan to allow for a half hour if possible because, well I am sure you know why. But I have done 15 mins in a hurry, and a couple a hours if not. Just be careful about leaving it out too long, but I have never had one last long enough to worry about it, (OH and don't forget to save those bones, bits & pieces for a gumbo!).
I mean the above link seems it was a 14 lb turkey, at 275 and it only took 4 and 1/2 hours. So I am sure you're close enough.
Remember with an AMPs to open the vent because like a fire place it needs to draw air thru, no air, no smoldering pellets in the AMPS. Once its smoking good, you can adjust the vent to fit your smoke. Or just leave it open this time, learn how to adjust it next time.
Don't forget to take some pictures so we can see what and how ya did.
Its not too hard, remember the cavemen could do it, just remember to relax, have patience, act like you know exactly what you are doing if anyone asks, and enjoy the smoke.
Oh and when ya get a chance, click the "My Profile" icon above on the tool bar and take a min., but if nothing else make sure and enter where you sleep at night so we'll all know. In a lot of conversations here it will make a difference. Thank you.