Once.
Mind you this takes me 15-20 minutes a session and I take my time. And I'm working my way up to 2 a day like this though, and the second one would be right before bed.
I used to do 3 a day every day, but this was with pronouncing the words wrong and as fast as possible (7-10 minutes a RTR). Make sure you're not only pronouncing the letters correctly but that you are taking enough time to do so. Spitting them out is only slightly faster, and if you need to get a Final RTR done quickly just do one rep of each letter.