Follow-up email for webinar sent day after, not five days after

I've been editing the html for our webinar emails, and it's all been working fine. But I had set up the follow-up email to attendees and absentees to go out five days after the webinar – I set this up in both the settings for the specific webinar, and in the Account Manager > Webinar Settings. This was to give me time to add the URL for the recording.

However, the email went out the day after the webinar (luckily, I'd put in a holding URL of a link to our YouTube channel).  I've checked and re-checked the settings and they all say five days after the webinar date. Any idea what's going wrong? I know it's almost certain to be user error, but dashed if I can find it.