Structurally (that is, grammatically), there seems nothing wrong with the sentence (other than the fact that "what" should be capitalized, and the period should go inside the quotation marks if you're going by American usage.
But "ephemeral" means "fleeting" or "transient," and it carries a strong implication of something delicate and difficult to catch, like the ghost of a butterfly. Is that what you want to say? It's also a bit too unusual and poetic for a casual statement like this; most people wouldn't use it in light conversation.
And perhaps more important, "rendezvous" carries the implication of two people meeting (often secretly) as lovers. I suspect you really don't mean that.