[It's probably somewhat of a suggestion in itself that Shun demonstrates no sign of moving out of the position even in the few moments it takes Ren to react, even if he partially just seems to be waiting for said reaction so he can consider his demonstration over. To him, it's not really anything more than another training move, and accordingly mundane even if it is a bit of an extreme one.

So while Ren's delight in seeing it isn't entirely unexpected given how Shun considers him to "overreact" to a lot of things regarding him, it does, for whatever reason, make him rethink letting the position drop. His immediate assumption of himself is that it's a proof of his skill, not that he really needs to give Ren that at this point, but somewhere in the mix there's an emotion he doesn't remember having felt in the last few years, and accordingly can't put a name to right now.

Dropping his arms from behind his back to cross them in front of him instead, Shun shrugs slightly.]

A while. I don't usually just do this sort of thing to see how long I can, but if I can hold myself at the roof of a room long enough for an ambush, this shouldn't be that much of a problem.