We know that in "Assignment: Earth", in 2268, the time travel method discovered in 2267 ("Tomorrow is Yesterday") is considered a standard research tool. In 2286, it's considered a reasonable technique to capture animals from 1986 Earth (ST IV: The Voyage Home): Kirk is charged with insubordination, not violating the Temporal Prime Directive.
In the Voyager episode "Timeless", we see that in a potential version of circa 2390 Chakotay and Kim are fleeing from charges including "conspiracy to violate the Temporal Prime Directive".
Do we know when, in this century-wide window, the Temporal Prime Directive first gets codified? Note that this is different from "when is the Temporal Prime Directive first expressed" because 29th century enforcement officers go back to various points in history and describe the directive to people, including possibly at times before the directive was codified.