Let's say you can do it once per long rest out of combat. You can do it a second time at level 10. Without a limitation of some sort, it would be far too easy to almost always pre-load a rocking combat spell ahead of time.
You leap over the banister, however, as you do so, your toe hooks on the edge of the rail and you end up landing hard on your knees, managing to catch yourself before you sprawl out onto your face.