That’s a good question.
On pg. 5, Fr. Gillespie remarks:
Fr. Gillespie, therefore, at least in one place, considers the initial twelve days to be a subcategory of preparation — I don’t believe he calls the twelve days a “preparation” as some authors do — and I would interpret his comment on pg. 27 in light of this. In other words, the “act of sacrifice that can be made over the remainder of the preparation period” should be an act one sets aside for the remainder of the 33 days.
Having said that, this is obviously not set in stone. I almost hate making comments like that, because it smacks of relativism, but the fact remains that Total Consecration can be made even without any preparation; and slightly tweaking one person’s approach to it is hardly going to make the whole process come to naught. (St. Louis de Montfort, as far as I am aware, didn’t require a consistent act of sacrifice as such; and frankly, while I respect some of the modern spiritual writers who have altered de Montfort’s method to varying degrees — like Fr. Gillespie or Fr. Gaitley — de Montfort is after all a Saint who attained sanctified perfection. de Montfort’s authority here outweighs that of his interpreters, IMHO.)
I would personally encourage you — for what little that is worth — to keep doing what you’ve been doing for the rest of the 33 days. If that proves too difficult, do what can be done without removing the challenge entirely.