From previous threads,
2018: Duke overenrolled, no WL movement
2019: April 30 PTE, WL As start 5/1
2020: April 30 PTE, WL As start 5/4
2021: Little movement, 2nd hand report on 5/11 about 5/1 acceptance.
2022: April 30 PTE, WL As start May 3
2023: April 30 PTE, WLs As start May 2.
For what it's worth, it seems like they usually take one business day after the PTE deadline to start WL acceptances if they don't overenroll.
I'm guessing that WLs A calls happen in the afternoon and evening because Dr. Yee (the only person who has called for WL As) has morning meetings or the admission, IT staff takes the morning to draft the admission letters, update the portal and AMCAS based on the list given to them after the adcom meeting yesterday. The admissions office people then provide Dr. Yee or whoever is calling with a list of phone numbers to call to notify admits in the afternoon.
Note: All of the above is just speculation by another anxious applicant on the WL.