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In my opinion, I don't think that the episode of Ven. Purana could have been the first real schism. The reasons are for a schism to occur, there should be a majority of people who disagree
to certain things like the Vinaya ( in the Second Buddhist Council) and not only one person ( in this case Ven. Purana).
Ven. Purana wouldn't participate because he might have understood the Teachings of Buddha according to his own interpretation and what he heard and understood seemed to be bit different from what was presided at the First Buddhist Council/Sangiti. His non-participation also indicated that there were different opinions existing then but it couldn't cause a schism yet. However, this could be a sign that a split or schism might occur in the future as what could be seem in the Second Buddhist Council. During the Second Buddhist Council, the majority were against the ten Vinaya rules. So a schism occurred and then two schools emerged which were the Staviravadins and Mahasanghikas.

In my opinion, I don't think that the episode of Ven. Purana could have been the first real schism. The reasons are for a schism to occur, there should be a majority of people who disagree
to certain things like the Vinaya ( in the Second Buddhist Council) and not only one person ( in this case Ven. Purana).
Ven. Purana wouldn't participate because he might have understood the Teachings of Buddha according to his own interpretation and what he heard and understood seemed to be bit different from what was presided at the First Buddhist Council/Sangiti. His non-participation also indicated that there were different opinions existing then but it couldn't cause a schism yet. However, this could be a sign that a split or schism might occur in the future as what could be seem in the Second Buddhist Council. During the Second Buddhist Council, the majority were against the ten Vinaya rules. So a schism occurred and then two schools emerged which were the Staviravadins and Mahasanghikas.

There are various opinions in early Buddhism regarding whether the Abhidhamma was actually chanted at the 1st Council. In fact, the reference in Theravada sources to an Abhidhamma in six books rather than seven, indicates an earlier version of what would later be compiled as seven.
Also note that the Abhidharma in seven books is attributed to authors other than the Buddha Himself. Frauwallner provides substantial evidence in his Sutides in Abhidharma that the Abhidhamma and Abhidharma share a common source, again suggesting that the 1st Council (if a historical fact) did not include the chanting of the Abhidhamma.

With regard to the time, I was under the impression it was three months, but will have to review my notes.

With regard to how they could have chanted all of the Tripitaka or even the Suttapitaka in any time frame, keep in mind that Ananda was not the Buddha's faithful assistant for all 45 years, that he would not have been privy (at least directly) to any teachings given to the gods (if these occurred) and that even in the records of the Theravada there is the account of the Elder Purana who abstained from ratifying the teachings as chanted at the 1st Council, preferring to continue following the dhamma as it had been taught to him.

Lamotte presents an excellent account of the councils in his History of Indian Buddhism, available here.

For some additional info on the 1st Council, you may want to review this brief article.