Until Christ. That’s the short answer. The Torah was added to the Covenant promises of Genesis 12 and 15 in order to put into bold relief for Israel its sinfulness. And Paul makes it clear in Romans 7:1 that he is speaking to Jewish converts: “I am speaking to those who know the law.” That is, to those who are tempted to think election means knowing the Law, when for Paul election means having the Law that reveals sin. But, then, once Christ comes, what happens to the Law?
Laws are binding during one’s lifetime. He uses an analogy: a woman is bound to marital fidelity during the lifetime of her marriage. If her husband dies, she is free to remarry.
The Torah had its lifetime: from Moses to Christ. Christ came, they belong to Christ; before then the Law was doing its work of revealing sin. “But now that we [he means here “Jewish Christians”] are discharged from the Law, dead to that which once held us captive, … so that we are slaves … in the new life of the Spirit.”
How long does the Law last? Until the Spirit comes.
How long does a typewriter last? Until you buy an Apple Powerbook. (A PC is the era of John the Baptist.)