By the Law of Contradiction, free will cannot be the case, as it would result in a contradiction. At exactly 1pm I can't equally decide to press or not press the letter "T" and decide to press the letter "T" at the same time. — RussellA

It sounds like you decided to contradict your decision and action at 1 pm from your free will. :D

demonstrate to me how introspection revealed to you that free will is an illusion, and you live in a deterministic world, — Metaphysician Undercover

I don't believe in particular that thoughts can cause themselves, and I don't believe in general in spontaneous self-causation.

One reason for my disbelief in spontaneous self-causation is that it is something I have never observed.

When I see a billiard ball on a billiard table start to move for no reason at all, then I may change my mind.
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No "reason why" is given for that law, it is stated as a descriptive fact — Metaphysician Undercover

Law of nature has more than one meaning.

It can be a description, as Newton's first law. From SEP - Laws of Nature

Science includes many principles at least once thought to be laws of nature: Newton’s law of gravitation, his three laws of motion, the ideal gas laws, Mendel’s laws, the laws of supply and demand, and so on.

It can be an explanation. As you wrote:

A "law of nature" in this sense necessarily precedes the event, because the laws of nature are what makes things act the way that they do. — Metaphysician Undercover

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However, I see no reason to discuss them if they are just proposed as reason to accept the illogical premise of contemporaneousness. — Metaphysician Undercover

One of the reasons I don't believe in free will is that it requires self-causation, where the thought one has is contemporaneous with the decision to have the thought.