Engagement Program Sent Timing with Timezone

I set up a new engagement program that sends an email on Monday & Thursday at 8:30am with time zone functionality enabled. The first batch of leads was about 1000 names, from various US timezone, and I imported the list into the Program on Sunday night in EDT. As of Monday morning, the first email was not sent to anybody in the program even after 12pm EDT. The program was on, the lead-level program status was marked as member, the cadence status was normal, so everything was on "green light". (and of course, the leads are marketable leads, i.e. not opted out, etc). I wonder what I missed during the setup, and I appreciate anyone's insight.