dieversary
The commemoration of a day that is exactly 24-hours since an event. From the Latin words "diem", meaning "day", and "vers(us)" meaning "to turn". Related to the words "anniversary" (exactly a year from the original date) and less frequently used "mensiversary" (exactly a month from the original date).
John celebrated his 10,000th dieversary by sitting in a cold, dark room, and listening to a specific Tool album on repeat.