Our guide, Russell Schubert told us about this flower. Moonflower buds such as this will open at dusk over a 20 minute period, just as it is getting really dark. Their only pollinator is a nocturnal moth. So, Teresa and I watched this one and it really happens as advertised. You can see a time-lapse in this movie: https://plantsinmotion.bio.indiana.edu/plantmotion/flowers/moonflower/moon.html

Beautiful to behold....