The fees are percentage based, so the investment interval doesn't matter. $5/day gets you a $0.15 fee, $35 a week is $1.05. It all nets out to the same dent made.
However, I just tried setting up a new transaction and the fee looks to be $0.99 for a $5 investment. At ~20%, this sort of averaging would no longer be worth it. Like I said before, I guess I've been grandfathered in after the new fees schedule was imposed. Let's see how long it lasts.