Usually we merge the new Kotlin into the upstream Compose repository within 24 hours of the Kotlin release going public*. Jetbrains Compose will then usually publish a release within a couple of days*. Google will then usually publish a release on the wednesday following an alternating wednesday after the release (so no sooner than a week later, no later than three weeks later, two weeks on average)*. So the short answer is that the latency for Desktop is usually a couple days and the latency for Google/Android is usually a couple weeks*.
* These dates do NOT constitute a commitment by Google nor Jetbrains; historical trends do not necessarily predict the future, workflows can change and unforeseen blocking bugs can happen, blah blah