This description is downplaying what's changing by a lot. The way you present it, they're merely adding a 24h wait time to the existing local "unknown sources" toggle.
They've been chipping away at AOSP for years, pulling more and more parts of the Android experience into their proprietary Google Play Services. In this case, they're doubling down in the same direction. Sure, it may be more or less transparent from a user-facing perspective, but it's a fundamental change to the model.
Previously, it was ultimately a local decision: Android warned you, you enabled the permission, and you installed the APK. It now becomes dependent on a Google-controlled verification/authorization mechanism. That's fundamentally different from making the existing "unknown sources" toggle more annoying.