Pretty sure the estimated days clearly states that it is if you sweep ALL of a ninja's elite instance (including those you haven't unlocked)
In case of Jirobo, there are 3 such instances, and being a 2 star ninja, he needs 30 frags to get. Estimation of 5 days would have been correct, as it would be 3x3=9 sweep per day, 45 sweep total, should drop around 30 frag.
I can't see whether or not there is an updated estimate thing, because I have all the ninjas from elite instance...