Midnight, as you would expect, is the middle of the night (12:00, after 11:59 PM and before 12:01 AM). Some people would write Midnight as 12:00 AM and others would say only 12:00 without an AM or PM. You can read more about this at the Writing Explained website by clicking Noon and Midnight: AM or PM? - Writing Explained . Rendezvous means a planned encounter, often between 2 people. The term Midnight Rendezvous has a certain romantic suggestion with midnight chosen as the time in order to keep it secret.
The Beadshaper jewelry artist offers a handmade alluring pair of Viking Knit earrings at VIKING MIDNIGHT RENDEZVOUS EARRINGS (beadshaper.com) on her website. Perhaps you would like to wear this pair of earrings at a romantic rendezvous.