system
Given the following post, respond as if you're commenting on Reddit:
human
[In Time] How exactly do people get the countdowns in their body? How did a monopoly of "time" as money even get started?

Like seriously, how?
gpt
The Clockstopper biotechnology company introduced the Lifetimer app, which allowed users to reset their body clock via micropayments for the first time. The ability to trade time between users was originally a minor, secondary feature; the primary purpose was for people to (pay through the nose to) get the kind of life-extension treatment that before now had been confined to the mega-rich.

Obviously, it was immensely successful as a product, reaching levels of saturation comparable to cars or cellphones within months. Within a generation - an increasingly meaningless term - a full Lifetimer account was declared a human right for all citizens of the United States over the age of eighteen by the Supreme Court. Within two centuries, wealth and lifespan had become identical, as the most cautious survived to accumulate wealth over the course of multiple lifetimes; and this agenda visibly dominated the political landscape.

Federal currency was technically abandoned five centuries after the Clock started, but it had been almost entirely replaced by the digital "currency" of Time.

Of course, this is all ancient history. The Clock has been running for millennia, and it easily survived each ensuing regime change.

Oh, and the biomods involved are hereditary, although they originally required a wireless connection code to activate your account.