I have found it useful to have more than one source to check things, so it may be worth your while to get an additional source.
Your question about when the tariff became effective is a valid one. I sometimes scan through old newspapers to get a sense of what is going on. Earlier this week, I did see an article that was published around the time of that March 18, 1861 article or slightly after it, that said the proposed Confederate tariff did not pass in some March vote. I imagine the proposed tariff had raised the concerns that the March 18 article had spoken about.
I read so many papers this past week and did not keep track of which date and which paper had said the proposed tariff had not passed. I did not make a copy of it at the time. A number of Northern papers did express concern about the effect of the Confederate tariff in March as various posters have cited over the years.
I think, but am not positive, that initially the Confederacy used the old 1857 US tariff before they finally got a slightly lower tariff law either passed and became effective. I do not have a timetable of the various Confederate efforts to pass or amend what they passed regarding their tariff.
Here's an article I found this morning in the Daily Patriot and Union of Harrisburg, Pennsylvania on March 27, 1861 [the paragraph breaks for readability and the bold emphasis parts are mine]:
We were told that a modification of the tariff was necessary for two reasons: First, to increase the revenue and replenish an exhausted Treasury; second, to afford adequate protection to domestic industry. These results might possibly have both been attained had the policy of the Republican party not caused the destruction of the Union.
But having broken the Union, the tariff i3 as worthless, for both purposes, as the paper upon which it is written. The schedule of the tariff adopted by the Confederate States exhibits about one-half the duties imposed by the Morrill tariff. Pig iron, for instance, which under our tariff pays a specific duty of from six to fifteen dollars per ton, is charged but five per cent, ad valorem by the Southern rates; and how are we to prevent the importation of foreign iron at the South, and its unrestricted transportation Northward, under the free intercourse prevailing between the States ? So with iron of every description, and every article of commerce imported from foreign countries. Entering Southern ports at one-half the rate they would be compelled to pay at the North, it will be impossible to prevent their spread over the country. The government would find it a huge undertaking to guard the line separating the Confederate States from the Union; and even if practicable, the cost would almost exceed the benefit.
It would be equally difficult to prevent the entry of vessels into Southern ports by a rigorous blockade; and the other remedy proposed—the abolition of these ports of entry—could not long bind foreign nations, whose immediate interests would compel them to recognize the de facto government established at the South, when they would claim and enforce free and unobstructed intercourse.
This conflict between the two tariffs must result in diminishing the revenue of our government, and in subjecting manufacturers to a flood of foreign competition, in comparison with which the old tariff, in a compact Union, was as nothing. Pennsylvania may thus comprehend the fearful retribution she has brought upon herself by neglecting the cause of the Union when assailed by its enemies, to clutch at the unreal, unsubstantial good of a protective tariff. She has purchased a worthless tariff at the expense of the Union.
If I recall correctly, the Confederate government fashioned its first tariff structure around Feb. 9.
It was announced about a month later. Immediately after, all sorts of newspaper outcries began...mostly calling for force to be used against the seceded states.
As you know, Lincoln had just taken office. Governors and Congressmen began a clamor to have him do something to coerce the South.
A pretty effective piece of anti-Republican propaganda, I'd say, which could well have been written by Pennsylvania's Doughface-in-Chief, former Democrat President Buchanan.
Of course it's all lies, just as is most of what spews out of Democrats.
The real truth is:
All written like true Democrats, ever eager to blame Republicans for their own malfeasance.
In fact, by their own words the Morrill Tariff proposal had nothing to do with Fire Eaters' declarations of secession.
What caused them to secede at pleasure was simple fear of what anti-slavery "Black Republicans" might somehow do in the future to threaten their "peculiar institution."