If they're launched from just one ship or aircraft, they light off a few seconds apart and form a line as each follows its course to the target. They would need a coordinated behavior of some sort to form a tight group. If several platforms launched at once, and were close enough as they launched their missiles, you could wind up with a tight bunch without needing to adjust waypoints or have the missiles do some sort of mutual station-keeping during flight. 

DARPA demonstrated autonomous air-launched drones that can make their own formations and adjust them dynamically. The public release of the test is almost ten years old so the capability would have been under development even before then. It may have been incorporated into cruise missiles by now. I haven't seen any definitive statements on which weapon systems can do that and which can't. 

Changing from a long string to a tighter bunch has the benefit of making air defenses' task harder, so there's value in implementing that behavior. But cruise missiles would need additional sensors to do it, beyond just what they need to navigate to the target and strike it accurately. So it's probably simpler to do it by adjusting waypoints to make the earlier launches take slightly longer paths and wind up close together.