It was hard to time a bulk e-mail that specifically.
You would get throttled by ISPs as an anti-spam measure, or maybe for bandwidth reasons, so the million emails might get received over an 8 hour period, when you really wanted them hit everyone’s inbox at 7:30am to be one of the first emails they saw in the morning (for example).
In reaction to that, the software to send the bulk emails started throttling them for you. If Gmail is going to throttle your one million emails, you might as well throttle them before they get to Gmail and stay on Gmail’s good side.
Long story short, it’s surprising that you would get an email like that every day at the same time. Maybe 1-800 Flowers is on a super white list and everything goes through when they hit send, or maybe you are in batch 1 and their software’s self-throttling always sends batch 1 right after midnight, and the numbers are low enough that nothing from batch 1 gets throttled by your ISP.
(You might as well just unsubscribe to save space in your inbox)