@mjk45: I do not know the absolute formula, however I do know that I killed Mark 64 (with a 5 star) and had all others 5 star'd up to that point when I had the 3 primary roles maxed out 2 of the side roles (for each character), 2 of my 3 characters had tier 2 weapons with 1 of them with the Ultimate (got really unlucky on Traps). I had all others 5 star'd up to that point before I killed number 64.
Also, my buddy only did the exact missions needed to get the growth egg, maxed out all 6 roles for each character and had his main three with ultimate weapons before he started 5 starring missions. He plat'd the game also, and told me he did not have any major problems. Id have to surmise that the timelimit is pretty closely linked ratio wise with characters strength/magic stats.
