Taken from Dharmawheel:
"In the country of Benares at Rsipatana in the Deer Park, the World-honored One first turned the wheel of doctrine, [teaching] the four holy truths for those setting out in the word-hearers' vehicle. This turning of the wheel was marvelous and wonderful, such as nobody, whether gods or men, had been able to turn in the world before. Nevertheless there were superior teachings, for [this first turning] had to be interpreted and occasioned controversy. Then the World-honored One with an underlying intent turned the wheel for the second time for the sake of those setting out in the great vehicle, [teaching] that all things have no-essence, no arising, and no passing away, are originally quiescent, and are essentially in cessation. This turning of the wheel was marvelous and wonderful indeed. Nevertheless there were teachings superior to this, for it also had to be interpreted and occasioned controversy. The World-honored One then with an explicit meaning for the third time turned the wheel of doctrine for those setting out in all the vehicles, [teaching] that all things have no-essence, no arising, and no passing away, are originally quiescent, and are essentially in cessation. This turning was the most marvelous and wonderful that had ever occurred in the world. It had no superior nor did it contain any implicit meaning nor occasion any controversy." (Samdhinirmocana Sutra, ch 5, p 49; tr. Keenan, BDK edition)
So, to sum up the teachings of the three turnings:
1. four holy truths for those setting out in the word-hearers' vehicle 2. all things have no-essence, no arising, and no passing away, are originally quiescent, and are essentially in cessation 3. all things have no-essence, no arising, and no passing away, are originally quiescent, and are essentially in cessation
The definitions of the second and third turnings are identical.
The same sutra also answers the question about the nature of the unconditioned.
"Good son, the term 'unconditioned' is also a word provisionally invented by the First Teacher. Now, if the First Teacher provisionally invented this word, then it is a verbal expression apprehended by imagination. And, if it is a verbal expression apprehended by imagination, then, in the final analysis, such an imagined description does not validate a real thing. Therefore, the unconditioned does not exist." (ch 2, p 12)
Lopon Namdrol (Malcolm Smith):
While it is certainly true that many people have understood it this way, for example, the Korean master Wan tshig (sorry, did not dig up his actual Korean name):
that Dharma of the Buddha is profound, nevertheless because there are
many methods of guidance and ways of introducing it, not only one, the
Sovereign of the Dharma taught three
Dharma wheels. Among those the first the demonstration of cycling in the
forests where wild animals roam who constantly perish and the causes
and results of nirvana to those who are to enter into the Śrāvakayāna.
This is called “The Dharmawheel of the four truths”.
Second, is teaching the Ārya-prajñāpāramita to sixteen gatherings at
Vulture Peak and so on to those who are to enter the Bodhisattvayāna.
This is called the Dharmawheel of characteristiclessness. The third is
the teaching of the Saṃdhinirmocana and so on to those in the pure
buddhafields such as Padmagarbha, and the impure ones to those are to
enter all vehicles called the “Mahāyāna of the definitive meaning”.
This is not completely certain. There is no record in any other sutra or commentary of where these sites may be. In any case, even if we accept Wan tshig's statement at face value, it still means that the Mahāyāna arose at the same time as the Śravakayāna because it was taught during the lifetime of the Buddha.
Moreover, there is no certain statement in the citation itself that this is the case. In his General Division of Tantras, Loppon Sonam Tsemo responds to the above assertion:
- If it is true those three
Dharmawheels were turned for different inclinations, to claim “…they
were turned in stages in different countries’” is not reasonable. If it
is asked how it is not reasonable, it is because scripture and reason
are contradicted, the objections of the srāvakas will not be rejected,
the Sugata will come under criticism and so on. Because there will be
many such faults, it is not reasonable.
He ultimately answers this qualm with the citation from the Sutralaṃkara:
- Not predicted earlier, arising at the same time.
As the Sandhivyākarana-tantra too states:
...the pleasing single vajra word
becomes many different [words]
from the perspective of the mentalities of the trainees.
A single statement of the Bhagavan’s will appear as many different Dharmas to many different trainees at the same time. That also does not contradict the citation of the Samdhinirmocana-sūtra explained above. Although that citation does state different Dharmas, it does not state different locations or different times. Since that is so, teaching different Dharmas to trainees with one statement made at the same time is called “the array of speech,” and demonstrating many different bodies in different locations at the same time are the beneficial deeds with an array of bodies.
There is really only one reference to the three turnings of the wheel in a single sutra. The Samdhinirmocana. The way I read the Samdhinirmocana is that it confirms the teaching found in the second turning and renders it indisputable.
The Bhagavan, well disclosing the correct entry into all vehicles, beginning from the nonexistence of the inherent existence of all phenomena, beginning from their absence of arising, absence of ceasing, being peaceful from the beginning, being parinirvana by nature, turned a third very amazing wheel of Dharma. This wheel of Dharma is unsurpassable, not circumstantial, of definitive meaning and indisputable.
This is hardly a smoking gun that confirms that you are basing your opinions on the so called third turning. Frankly, there is virtually no attention this teaching in the Indian canon, though a big deal about it is made in Tibetan and Chinese Buddhism. The idea that the three turnings are based on three distinct historical epochs is rejected out of hand by such India scholars as Dharmamitra in his Abhisamayālaṃkārakārikāprajñāpāramitopadeśaśāstraṭīkā prasphuṭapadā.