hey

Make sure you're on patch 1.27. It won't work on more recent patches. You can save warp at any time, not just right after a mission.

You do the complications savewarp by making a quicksave file and reloading it. As soon as the loading screen pops up, hold F6 (or whatever you have as Franklin's character swap hotkey). Keep holding it until the game loads. You'll see Michael, and the map around him will be missing most textures. Let go immediately and you'll be teleported to Michael's safehouse. Most likely, you're on the wrong patch.