Don't ask him as if you suspect he doesn't know, just ask him as if you don't know and need to have it explained and then you'll know. Whether you can reasonably do that without offending him would depend how your previous conversation went. If it's not possible to ask without causing offence then don't. Regardless, it is registered nocturnal. Just watch yours when it flowers and see when the blooms open. I don't still have mine, unfortunately.
